netlink: Reset portid after netlink_insert failure

The commit c5adde94 ("netlink:
eliminate nl_sk_hash_lock") breaks the autobind retry mechanism
because it doesn't reset portid after a failed netlink_insert.

This means that should autobind fail the first time around, then
the socket will be stuck in limbo as it can never be bound again
since it already has a non-zero portid.

Fixes: c5adde94 ("netlink: eliminate nl_sk_hash_lock")
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -1081,6 +1081,7 @@ static int netlink_insert(struct sock *sk, u32 portid)
 	if (err) {
 		if (err == -EEXIST)
 			err = -EADDRINUSE;
+		nlk_sk(sk)->portid = 0;
 		sock_put(sk);
 	}