netlink: Reset portid after netlink_insert failure

The commit c5adde9468b0714a051eac7f9666f23eb10b61f7 ("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: c5adde9468b0 ("netlink: eliminate nl_sk_hash_lock")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index dbe8859..bf6e766 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1081,6 +1081,7 @@
 	if (err) {
 		if (err == -EEXIST)
 			err = -EADDRINUSE;
+		nlk_sk(sk)->portid = 0;
 		sock_put(sk);
 	}