Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Remove support for FreeBSD 4.x and below.

Transform tbr_dequeue into a function pointer in order to build drivers with
ALTQ enabled versions of IFQ_* macros by default, as requested by serveral
others. This is a follow-up to the quick fix I committed yesterday which
turned off the ALTQ checks for non-ALTQ kernels.

Add an additional queue which will be "owned by the driver". This allows to
rig a PREPEND macro for ALTQ as the POLL/DEQUEUE semantic is very bad in
terms of locking. We make this a full functional queue to allow "bulk
dequeue" which will further reduce the locking overhead (for non-altq
enabled devices). Drivers will access this via the following macros, which
will show up in <net/if_var.h> once we expose ALTQ to the build:

IFQ_DRV_DEQUEUE(ifq, m) - takes a mbuf off the queue (driver queue first)
IFQ_DRV_PREPEND(ifq, m) - pushes a mbuf back to the driver queue
IFQ_DRV_PURGE(ifq) - drops all packets in both queues
IFQ_DRV_IS_EMPTY(ifq) - checks for pending mbufs in either queue

One has to make sure that the first three are protected by a driver mutex.
At the moment most network drivers still require Giant, so this is not an
issue. Even those that have thier own mutex usually hold it in if_start and
the like, so this requirement is almost always satisfied.

This evolved from a discussion with Andrew Gallatin.

This commit was generated by cvs2svn to compensate for changes in r130365,
which included commits to RCS files with non-trunk default branches.

Import parts of the ALTQ framework from latest KAME snapshot (which is up to
HEAD at this point). This will not exactly live in a vendor branch, but have
the vendor backing to make it easier to exchange diffs.

This will be followed by a diff which takes most of the .c files off the
vendor branch in order to:
- add locking
- disable ALTQ3_COMPAT code (which is outdated and "un-lockable")

There is work in progress to refine the configuration API. Import this "as
is" now to have more exposure time before 5-STABLE.

This is only the import, it will be some more days until you will actually
be able to compile ALTQ support into your kernel so don't hold your breath.
HEADUPs will be posted on current@ and net@ before this is actually enabled.

No-objection: re(scottl), core(rwatson)