rpc: fix getsockopt for LOCAL_PEERCRED on Mac OS X

This fixes the following error:
  error : virGetUserEnt:703 : Failed to find user record for uid '32654'

'32654' (it's random and varies) comes from getsockopt with
LOCAL_PEERCRED option. getsockopt returns w/o error but seems
to not set any value to the buffer for uid.

For Mac OS X, LOCAL_PEERCRED has to be used with SOL_LOCAL level.
With SOL_LOCAL, getsockopt returns a correct uid.

Note that SOL_LOCAL can be found in
/System/Library/Frameworks/Kernel.framework/Versions/A/Headers/sys/un.h.
Signed-off-by: NRyota Ozaki <ozaki.ryota@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/rpc/virnetsocket.c

@@ -1159,7 +1159,11 @@ int virNetSocketGetUNIXIdentity(virNetSocketPtr sock,
     socklen_t cr_len = sizeof(cr);
     virObjectLock(sock);
 
+# if defined(__APPLE__)
+    if (getsockopt(sock->fd, SOL_LOCAL, LOCAL_PEERCRED, &cr, &cr_len) < 0) {
+# else
     if (getsockopt(sock->fd, SOL_SOCKET, LOCAL_PEERCRED, &cr, &cr_len) < 0) {
+# endif
         virReportSystemError(errno, "%s",
                              _("Failed to get client socket identity"));
         virObjectUnlock(sock);