[NET] NETNS: Omit sock->sk_net without CONFIG_NET_NS.

Introduce per-sock inlines: sock_net(), sock_net_set()
and per-inet_timewait_sock inlines: twsk_net(), twsk_net_set().
Without CONFIG_NET_NS, no namespace other than &init_net exists.
Let's explicitly define them to help compiler optimizations.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index ee9dd83..2712544 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -869,7 +869,7 @@
 	struct sock *sk;
 	ax25_cb *ax25, *oax25;
 
-	sk = sk_alloc(osk->sk_net, PF_AX25, GFP_ATOMIC,	osk->sk_prot);
+	sk = sk_alloc(sock_net(osk), PF_AX25, GFP_ATOMIC,	osk->sk_prot);
 	if (sk == NULL)
 		return NULL;