firewall: revert to Asus's own NAT loopback for now - it's (only) partly broken at the moment, while ours doesn't work at all anymore
firewall: fixed incorrect GPL merge related to PPTPD CTF bypass, and ip6tables handling of new IPv6 connections on MIPS
firewall: synced formatting with GPL code for easier maintaining; fixed url filtering/keyword filtering support when CTF is enabled
firewall: re-added missing variable used by Asus's NAT loopback code
firewall: remove disabled code that was completely removed from GPL