netfilter: nf_log_bridge: merge with nf_log_syslog

Provide bridge log support from nf_log_syslog.

After the merge there is no need to load the "real packet loggers",
all of them now reside in the same module.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>