we used to handle the vlan tag etc insertion very very very late,

on al already ass embed ethernet frame, which meant:
-copy (most of) the existing ethernet header into a ether_vlan_header
on the stack
-fill the extra fields in ether_vlan_header
-set the ether type
-m_adj() to make room for the extra space ether_vlan_header needs
-m_copyback the ether_vlan_header into the mbuf
that involves moving data around, which isn't all that cheap.
cleaner & easier to have ether_output prepend the ether_vlan_header instead
of the regular ethernet header, which makes the vlan tagging essentially
free in most cases.
help & ok reyk, naddy; waste of time bikeshedding tech@

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