netfilter: nfnetlink_queue: Unregister pernet subsys in case of init failure

Commit 3bfe0498 ("netfilter: nfnetlink_{log,queue}:
Register pernet in first place") reorganised the initialisation
order of the pernet_subsys to avoid "use-before-initialised"
condition. However, in doing so the cleanup logic in nfnetlink_queue
got botched in that the pernet_subsys wasn't cleaned in case
nfnetlink_subsys_register failed. This patch adds the necessary
cleanup routine call.

Fixes: 3bfe0498 ("netfilter: nfnetlink_{log,queue}: Register pernet in first place")
Signed-off-by: Nikolay Borisov <kernel@kyup.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>