if_em problems, both 7 and 8-stable

[Pete Carah]

I cannot successfully create a vlan on if_em on either releng 7 or 
releng 8; I have seen a patch for part of
the problem (checksum offsets end up incorrect) but not all.  Even 
turning off ALL hw_xxx flags leaves one
unacceptable bug - the interface gets hard-reset any time you add or 
delete a vlan.  I *know* that cisco
uses these interfaces without these problems, so it has to be possible.  
I have used vlans in linux without
appearing to get the same problems, though I'm not sure the rest of the 
configuration matches.

What gives, especially since the patch for one of the problems (wrong 
checksum offsets) was generated
about 6 months ago...

We are trying to use an intel platform as a router; this is a 
show-stopper.  I could try linux though I prefer not to...

-- Pete