netfilter: xt_TRACE: add explicitly nf_logger_find_get call

Consider such situation, if nf_log_ipv4 kernel module is not installed,
and the user add a following iptables rule:
  # iptables -t raw -I PREROUTING -j TRACE

There will be no trace log generated until the user install nf_log_ipv4
module manully. So we should add request related nf_log module
appropriately here.

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>