[NETNS]: Consolidate kernel netlink socket destruction.

Create a specific helper for netlink kernel socket disposal. This just
let the code look better and provides a ground for proper disposal
inside a namespace.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Tested-by: Alexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 29fef55..626a582 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1405,6 +1405,17 @@
 }
 EXPORT_SYMBOL(netlink_kernel_create);
 
+
+void
+netlink_kernel_release(struct sock *sk)
+{
+	if (sk == NULL || sk->sk_socket == NULL)
+		return;
+	sock_release(sk->sk_socket);
+}
+EXPORT_SYMBOL(netlink_kernel_release);
+
+
 /**
  * netlink_change_ngroups - change number of multicast groups
  *