dhcp: stop obsessing over bridges
dhcp: stop obsessing over bridges

It's really not nice to fudge a link-local in dhcp code as the
bridge has a separate setting for it since 2019.

While here remove the restriction for bridge members on relay
that seems to originate from m0n0wall and abandoned by pfSense
in 2020.

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core