Make radix lookup on src and dst flow addresses optional

Make radix lookup on src and dst flow addresses optional
and configurable on per-interface basis.
Remove __inline__ for several functions being called once per
flow (e.g once per 10-20 packets on common traffic flows).
Update manual page to simplify search for BPF data link types.

Sponsored by Yandex LLC

Reviewed by:      glebius
Approved by:      ae(mentor)
MFC after:        2 weeks