MP-safe ifnet with psz & psref

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

Hi,

This proposal is the first step toward making interfaces
(struct ifnet) MP-safe; it applies psz and psref to ifnet
and ifnet_list to safely look up ifnets from ifnet_list
and safely remove an ifnet.

Here is a patch:
  http://www.netbsd.org/~ozaki-r/psref-ifnet.diff

One concern is m_reclaim that can be run in hardware
interrupt and so the patch skips if_drain if it's
running in hardware interrupt because pserialize is
basically designed used in lwp or softint (and now
psref is used with IPL_SOFTNET). Is there a better
solution?

And any other suggestions and comments would be
appreciated.

Thanks,
  ozaki-r

P.S. From today for ten days, I'll be unable to use
my main development machines, I wouldn't be able to
update and test patches reflected your feedbacks enough.