[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: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David 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;