netfilter: nf_log: get rid of XT_LOG_* macros

nf_log is used by both nftables and iptables, so use XT_LOG_XXX macros
here is not appropriate. Replace them with NF_LOG_XXX.

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