[NET]: Add a network namespace parameter to struct sock

Sockets need to get a reference to their network namespace,
or possibly a simple hold if someone registers on the network
namespace notifier and will free the sockets when the namespace
is going to be destroyed.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/inet_timewait_sock.h

@@ -115,6 +115,7 @@ struct inet_timewait_sock {
 #define tw_refcnt		__tw_common.skc_refcnt
 #define tw_hash			__tw_common.skc_hash
 #define tw_prot			__tw_common.skc_prot
+#define tw_net			__tw_common.skc_net
 	volatile unsigned char	tw_substate;
 	/* 3 bits hole, try to pack */
 	unsigned char		tw_rcv_wscale;

include/net/sock.h

@@ -105,6 +105,7 @@ struct proto;
  *	@skc_refcnt: reference count
  *	@skc_hash: hash value used with various protocol lookup tables
  *	@skc_prot: protocol handlers inside a network family
+ *	@skc_net: reference to the network namespace of this socket
  *
  *	This is the minimal network layer representation of sockets, the header
  *	for struct sock and struct inet_timewait_sock.
@@ -119,6 +120,7 @@ struct sock_common {
 	atomic_t		skc_refcnt;
 	unsigned int		skc_hash;
 	struct proto		*skc_prot;
+	struct net	 	*skc_net;
 };
 
 /**
@@ -195,6 +197,7 @@ struct sock {
 #define sk_refcnt		__sk_common.skc_refcnt
 #define sk_hash			__sk_common.skc_hash
 #define sk_prot			__sk_common.skc_prot
+#define sk_net			__sk_common.skc_net
 	unsigned char		sk_shutdown : 2,
 				sk_no_check : 2,
 				sk_userlocks : 4;