init: Fix dropping privileges in nflog runmode

init: Fix dropping privileges in nflog runmode

Using the run-as configuration option with the nflog capture method
results in the following error during the startup of suricata:
[ERRCODE: SC_ERR_NFLOG_BIND(248)] - nflog_bind_pf() for AF_INET failed

This is because SCDropMainThreadCaps does not have any capabilities
defined for the nflog runmode (unlike other runmodes). Therefore, apply
the same capabilities to the nflog runmode that are already defined for
the nfqueue runmode. This has been confirmed to allow suricata start
and drop its privileges in the nflog runmode.

Fixes redmine issue #3265.

Signed-off-by: Timo Sigurdsson <public_timo.s@silentcreek.de>