[NETLINK]: Check netlink_insert in kernel_create

This patch checks the return value of netlink_insert() in
netlink_kernel_create().  It could fail if someone loads
the same module twice for instance.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -868,7 +868,10 @@ netlink_kernel_create(int unit, void (*input)(struct sock *sk, int len))
 	if (input)
 		nlk_sk(sk)->data_ready = input;
 
-	netlink_insert(sk, 0);
+	if (netlink_insert(sk, 0)) {
+		sock_release(sock);
+		return NULL;
+	}
 	return sk;
 }