Clarify throughout the vlan(4) code the difference between a "tag" (the

Clarify throughout the vlan(4) code the difference between a "tag" (the
802.1q-defined 16-bit VID, CFI, and PCP field in host by order) and a
VLAN ID (VID).  Tags go in packets.  VIDs identify VLANs.

No functional change is intended, so this should be safe to MFC.  Further
cleanup with functional changes will be committed separately (for example,
renaming vlan_tag/vlan_tag_p, which modify the KPI and KBI).

Reviewed by:	bz
Sponsored by:	ADARA Networks, Inc.
MFC after:	3 days