netlink: use the appropriate namespace pid

This was included in OpenVZ kernels but wasn't integrated upstream.
>From git://git.openvz.org/pub/linux-2.6.24-openvz:

	commit 5c69402f18adf7276352e051ece2cf31feefab02
	Author: Alexey Dobriyan <adobriyan@openvz.org>
	Date:   Mon Dec 24 14:37:45 2007 +0300

	    netlink: fixup ->tgid to work in multiple PID namespaces
Signed-off-by: Tom Goff <thomas.goff@boeing.com>
Acked-by: Alexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -545,7 +545,7 @@ static int netlink_autobind(struct socket *sock)
 	struct hlist_head *head;
 	struct sock *osk;
 	struct hlist_node *node;
-	s32 pid = current->tgid;
+	s32 pid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;