move msghdr and cmsghdr out of bits/socket.h

these structures can now be defined generically in terms of endianness
and long size. previously, the 32-bit archs all shared a common
definition from the generic bits header, and each 64-bit arch had to
repeat the 64-bit version, with endian conditionals if the arch had
variants of each endianness.

I would prefer getting rid of the preprocessor conditionals for
padding and instead using unnamed bitfield members, like commit
9b2921be did for struct timespec.
however, at present sendmsg, recvmsg, and recvmmsg need access to the
padding members by name to zero them. this could perhaps be cleaned up
in the future.

arch/aarch64/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1, msg_iovlen;
-#else
-	int msg_iovlen, __pad1;
-#endif
-	void *msg_control;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad2;
-	socklen_t msg_controllen;
-#else
-	socklen_t msg_controllen;
-	int __pad2;
-#endif
-	int msg_flags;
-};
-
-struct cmsghdr {
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1;
-	socklen_t cmsg_len;
-#else
-	socklen_t cmsg_len;
-	int __pad1;
-#endif
-	int cmsg_level;
-	int cmsg_type;
-};

arch/generic/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen;
-	void *msg_control;
-	socklen_t msg_controllen;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int cmsg_level;
-	int cmsg_type;
-};

arch/mips/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen;
-	void *msg_control;
-	socklen_t msg_controllen;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int cmsg_level;
-	int cmsg_type;
-};
-
 #define SOCK_STREAM    2
 #define SOCK_DGRAM     1
 

arch/mips64/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1, msg_iovlen;
-#else
-	int msg_iovlen, __pad1;
-#endif
-	void *msg_control;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad2;
-	socklen_t msg_controllen;
-#else
-	socklen_t msg_controllen;
-	int __pad2;
-#endif
-	int msg_flags;
-};
-
-struct cmsghdr {
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1;
-	socklen_t cmsg_len;
-#else
-	socklen_t cmsg_len;
-	int __pad1;
-#endif
-	int cmsg_level;
-	int cmsg_type;
-};
-
 #define SOCK_STREAM    2
 #define SOCK_DGRAM     1
 #define SOL_SOCKET     65535

arch/mipsn32/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen;
-	void *msg_control;
-	socklen_t msg_controllen;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int cmsg_level;
-	int cmsg_type;
-};
-
 #define SOCK_STREAM    2
 #define SOCK_DGRAM     1
 

arch/powerpc/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen;
-	void *msg_control;
-	socklen_t msg_controllen;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int cmsg_level;
-	int cmsg_type;
-};
-
 #define SO_DEBUG        1
 #define SO_REUSEADDR    2
 #define SO_TYPE         3

arch/powerpc64/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1, msg_iovlen;
-#else
-	int msg_iovlen, __pad1;
-#endif
-	void *msg_control;
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad2;
-	socklen_t msg_controllen;
-#else
-	socklen_t msg_controllen;
-	int __pad2;
-#endif
-	int msg_flags;
-};
-
-struct cmsghdr {
-#if __BYTE_ORDER == __BIG_ENDIAN
-	int __pad1;
-	socklen_t cmsg_len;
-#else
-	socklen_t cmsg_len;
-	int __pad1;
-#endif
-	int cmsg_level;
-	int cmsg_type;
-};
-
 #define SO_DEBUG        1
 #define SO_REUSEADDR    2
 #define SO_TYPE         3

arch/riscv64/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen, __pad1;
-	void *msg_control;
-	socklen_t msg_controllen;
-	int __pad2;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int __pad1;
-	int cmsg_level;
-	int cmsg_type;
-};

arch/s390x/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int __pad1, msg_iovlen;
-	void *msg_control;
-	int __pad2;
-	socklen_t msg_controllen;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	int __pad1;
-	socklen_t cmsg_len;
-	int cmsg_level;
-	int cmsg_type;
-};

arch/x86_64/bits/socket.h

-struct msghdr {
-	void *msg_name;
-	socklen_t msg_namelen;
-	struct iovec *msg_iov;
-	int msg_iovlen, __pad1;
-	void *msg_control;
-	socklen_t msg_controllen, __pad2;
-	int msg_flags;
-};
-
-struct cmsghdr {
-	socklen_t cmsg_len;
-	int __pad1;
-	int cmsg_level;
-	int cmsg_type;
-};

include/sys/socket.h

@@ -19,6 +19,40 @@ extern "C" {
 
 #include <bits/socket.h>
 
+struct msghdr {
+	void *msg_name;
+	socklen_t msg_namelen;
+	struct iovec *msg_iov;
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
+	int __pad1;
+#endif
+	int msg_iovlen;
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
+	int __pad1;
+#endif
+	void *msg_control;
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
+	int __pad2;
+#endif
+	socklen_t msg_controllen;
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
+	int __pad2;
+#endif
+	int msg_flags;
+};
+
+struct cmsghdr {
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __BIG_ENDIAN
+	int __pad1;
+#endif
+	socklen_t cmsg_len;
+#if __LONG_MAX > 0x7fffffff && __BYTE_ORDER == __LITTLE_ENDIAN
+	int __pad1;
+#endif
+	int cmsg_level;
+	int cmsg_type;
+};
+
 #ifdef _GNU_SOURCE
 struct ucred {
 	pid_t pid;