Remove code to disable IFCAP_VLAN_HWFILTER by default for ixgbe(4) as VLAN
events are passed through by lagg(4) ever since r203548. Deactivation of
this capability by default due to lagg(4) was already not done for ixgbev(4)
and has been - although inadvertently - broken when em(4)/igb(4)/lem(4) and
ixl(4) were converted to iflib(9) in r311849 and r335338 respectively.

Reviewed by: erj
Differential Revision: https://reviews.freebsd.org/D15720 (part of)