Fix for kern/141646: when stacking pseudo drivers like
lagg and vlan the vlan attach/detach event is not being
handed down to em, this caused some init code not to run,
and thus VLANs did not work. Ultimately having the event
get propagated would be nice, but for now the solution is
to have HWFILTER off by default, when this is the case
VLANs will work, ifconfig can be used to turn it on and
then get HW tag filtering.