rx: Reorganise transmit queue walk

rx: Reorganise transmit queue walk

The transmit queue is stored in the order that we transmitted the
packets (by sequence number). This means that we can do all of the
ACK processing by just doing a single walk of this queue, rather
than having to walk the queue multiple times, once for each type of
ACK.

This clarifies the queue processing, and should reduce the amount of
time that we spending iterating large transmit queues.

Change-Id: I59578956e81197bbea7ce496e2f520a2995a3e95
Reviewed-on: http://gerrit.openafs.org/4796
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>