netfilter: cttimeout: put back l4proto when replacing timeout policy

We forget to call nf_ct_l4proto_put when replacing the existing
timeout policy. Acctually, there's no need to get ct l4proto
before doing replace, so we can move it to a later position.

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>