{ether,ieee80211}_ifdetach() can't be called with serializer being held, since

{ether,ieee80211}_ifdetach() can't be called with serializer being held, since
they will go through code which tries to hold serializer again, e.g.
ether_ifdetach() -> if_detach() -> in_control()

So in various NICs' xxx_detach():
- Move bus_teardown_intr() under "(device_is_attached())", whenever it is
  applicable.  Since it is not possible that intrhandle is NULL here, nuke
  original "(intrhandle != NULL)".  This can:
    1) Avoid holding serializer, if xxx_attach() fails
    2) Release serializer ASAP
    3) Ease following tasks
- Hold serializer only for xxx_stop()(or similar functions which stops NIC) and
  bus_teardown_intr()
- Call {ether,ieee80211}_ifdetach() after serializer is released

Other stuffs:
- Serialize xxx_detach() for awi(4), ep(4), sn(4) and xe(4)
- Release serializer before returning from {ed_pccard,ray}_detach()
- Make ipw(4)'s ipw_detach() suitable for error handling, adjust ipw_attach()
  accordingly
- Fix a bug in ex_pccard_detach(): instead of if_detach(), ether_ifdetach()
  should be used here
- For ndis(4), "ifp->serializer" ==> "ifp->if_serializer"
  Reported-by: esmith <esmith@postmark.net>
Discussed-with: dillon and joerg
Partially-Reviewed-by: dillon and joerg
Reported-by: Steve Mynott <steve.mynott@gmail.com> and me