netlink: Add missing goto statement to netlink_insert

The backport of 1f770c0a ("netlink:
Fix autobind race condition that leads to zero port ID") missed a
goto statement, which causes netlink to break subtly.

This was discovered by Stefan Priebe <s.priebe@profihost.ag>.

Fixes: 4e277624 ("netlink: Fix autobind race condition that...")
Reported-by: Stefan Priebe <s.priebe@profihost.ag>
Reported-by: Philipp Hahn <pmhahn@pmhahn.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/netlink/af_netlink.c

@@ -1118,6 +1118,7 @@ static int netlink_insert(struct sock *sk, u32 portid)
 		if (err == -EEXIST)
 			err = -EADDRINUSE;
 		sock_put(sk);
+		goto err;
 	}
 
 	/* We need to ensure that the socket is hashed and visible. */