Take a first cut at cleaning up ifnet removal and multicast socket

panics, which occur when stale ifnet pointers are left in struct
moptions hung off of inpcbs:

- Add in_ifdetach(), which matches in6_ifdetach(), and allows the
  protocol to perform early tear-down on the interface early in
  if_detach().

- Annotate that if_detach() needs careful consideration.

- Remove calls to in_pcbpurgeif0() in the handling of SIOCDIFADDR --
  this is not the place to detect interface removal!  This also
  removes what is basically a nasty (and now unnecessary) hack.

- Invoke in_pcbpurgeif0() from in_ifdetach(), in both raw and UDP
  IPv4 sockets.

It is now possible to run the msocket_ifnet_remove regression test
using HEAD without panicking.

MFC after:	3 days

0 files changed, 0 insertions, 0 deletions