vlan: Respect IFCAP_LRO mask

vlan_capabilities(), used by the IFCAP ioctl, was not respecting the
IFCAP_LRO bit if it was masked by the requestor.

This prevented if_bridge(4) from automasking LRO with a message like:
bridge0: can't disable some capabilities on em3.11: 0x400

This also prevented manually disabling LRO from any vlan interface.

PR: 254596
Reported by: Paul Vixie <paul@redbarn.org>
MFC after: 1 week