netfilter: nft_synproxy: unregister hooks on init error path

commit 2b4e5fb4 upstream.

Disable the IPv4 hooks if the IPv6 hooks fail to be registered.

Fixes: ad49d86e

 ("netfilter: nf_tables: Add synproxy support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>