netlink: Add missing goto statement to netlink_insert

netlink: Add missing goto statement to netlink_insert

The backport of 1f770c0a09da855a2b51af6d19de97fb955eca85 ("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: 4e2776241766 ("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>