[NETNS]: Add netns refcnt debug for kernel sockets.

Protocol control sockets and netlink kernel sockets should not prevent the
namespace stop request. They are initialized and disposed in a special way by
sk_change_net/sk_release_kernel.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1314,7 +1314,7 @@ void sock_net_set(struct sock *sk, struct net *net)
 static inline void sk_change_net(struct sock *sk, struct net *net)
 {
 	put_net(sock_net(sk));
-	sock_net_set(sk, net);
+	sock_net_set(sk, hold_net(net));
 }
 
 extern void sock_enable_timestamp(struct sock *sk);

net/core/sock.c

@@ -1001,6 +1001,7 @@ void sk_release_kernel(struct sock *sk)
 
 	sock_hold(sk);
 	sock_release(sk->sk_socket);
+	release_net(sock_net(sk));
 	sock_net_set(sk, get_net(&init_net));
 	sock_put(sk);
 }