X700 family of controllers has limited number of available VLAN
HW filters. Driver did not handle properly a case when user
assigned more VLANs to the interface which had all filters
already in use. Fix that by disabling HW filtering when
it is impossible to create filters for all requested VLANs.
Keep track of registered VLANs using bitstring to be able
to re-enable HW filtering when number of requested VLANs
drops below the limit.

Also switch all allocations to use M_IXL malloc type
to ease detecting memory leaks in the driver.