rx: Generate BUSY packets for error call channels

rx: Generate BUSY packets for error call channels

Currently, if a call is error'd out but still active, we won't
generate BUSY packets if another call comes in on the same channel.
This is because we bail out earlier, here, before we get to the BUSY
processing.

The comments suggest that this is for if we enter an error state while
waiting for TQ to clear. So, only do this if our error has changed.

Reviewed-on: http://gerrit.openafs.org/8460
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Simon Wilkinson <simonxwilkinson@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry-picked from commit a84c6b0ece1fdee4f462c6ce27fa78c2e0d419f4)

Change-Id: I50fda40b3f010f1b9d03f2d3e22ed00381ae0b33
Reviewed-on: http://gerrit.openafs.org/8548
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: BuildBot <buildbot@rampaginggeek.com>