rx: Fix non-TSFPQ rxi_FreePackets

rx: Fix non-TSFPQ rxi_FreePackets

Actually count the number of packets we're given, so we don't bail out
early because num_pkts is 0. Without this, we effectively do not free
most packets for non-pthreads Rx, so e.g. the unix kernel module will
leak memory quite quickly and be very slow.

This was introduced by 170dbb3c.

Change-Id: Id781e37170683c422b40079fdda018be1caddaf3
Reviewed-on: http://gerrit.openafs.org/8401
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <simonxwilkinson@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>