Rework packet direction detection based on dynamically learned addresses

[mlasch]

Local and remote address distinction is based on hard coded IP addresses. This should be implemented with netlink and rtnetlink in order to learn about addresses used in the system.

• SRC addr is in local net of one of the interfaces and DST is not local ➡️ OUTBOUND
• DST addr is local net of one of the interfaces and SRC is not local ➡️ INBOUND
• DST and SRC are local ➡️ local traffic, ignore
• DST and SRC are not local ➡️ should not happen on a SOHO router, ignore or log error