tap(4): allow full-duplex and non-zero speed

tap(4) devices advertise themselves as just 'ethernet autoselect',
without duplex or speed capabilities.
This advertisement makes them unable to be aggregated into lacp-based
lagg(4):

• lacp code requires underlying interfaces to be full-duplex, else interface will not participate in lacp at all
• lacp code requires underlying interface to have non-zero speed, else this interface can not be selected as active aggregator

PR: 217374
Reported-by: Alexandre Snarskii <snar@snar.spb.ru>
Co-authored-by: Mina Galić <freebsd@igalic.co>
Reviewed-by: imp,karles
Pull-request: https://github.com/freebsd/freebsd-src/pull/745