HEADSUP: MPSAFE network drivers

I'm committing changes to mark various network drivers' interrupt handlers 
MPSAFE. To insure folks have a way to backout if they hit problems I've also 
added a tunable that lets you disable this w/o rebuilding your kernel.  By 
default all network drivers that register an interrupt handler INTR_MPSAFE 
are setup to run their ISR w/o Giant.  If you want to defeat this w/o 
changing the code you can set

debug.mpsafenet=0

from the loader when booting and the MPSAFE bit will automatically be removed.  
I plan to use this to also control forthcoming changes for registering MPSAFE 
netisrs.

The following drivers are marked MPSAFE:

ath, em, ep, fxp, sn, wi, sis

I've got changes coming for bge.  Other drivers probably can be marked MPSAFE 
but I'm only doing it for those drivers that I can test.

	Sam

attached mail follows:

attached mail follows:

  FreeBSD src repository

  Modified files:
    sys/kern             subr_bus.c 
  Log:
  Add a temporary mechanism to disble INTR_MPSAFE from network interface
  drivers.  This is prepatory to running more parts of the network system
  w/o Giant.
  
  Revision  Changes    Path
  1.135     +13 -0     src/sys/kern/subr_bus.c
http://cvsweb.FreeBSD.org/src/sys/kern/subr_bus.c.diff?r1=1.134&r2=1.135