build: use -fno-omit-frame-pointer for ease of debug

We are not a performance sensitive program and this helps debugging in
many situations.
interfaces: document and test pattern matching
interfaces: allow whitelisting an interface

Currently, this means that an interface can be both blacklisted and
whitelisted and in this case, it is accepted as valid.
interfaces: circumvent any physical check on exact match

When enabling an interface with `-I eth0`, any physical check will be
circumvented. This allows lldpd to send and receive on VLAN interfaces.