IB/srp: Avoid endless SCSI error handling loop

If a SCSI command times out it is passed to the SCSI error
handler. The SCSI error handler will try to abort the commands that
timed out.  If aborting fails, a device reset will be attempted.  If
the device reset also fails a host reset will be attempted.  If the
host reset also fails the whole procedure will be repeated.

srp_abort() and srp_reset_device() fail for a QP in the error state.
srp_reset_host() fails after host removal has started.  Hence if the
SCSI error handler gets invoked after host removal has started and
with the QP in the error state an endless loop will be triggered.

Modify the SCSI error handling functions in ib_srp as follows:
- Abort SCSI commands properly even if the QP is in the error state.
- Make srp_reset_host() reset SCSI requests even after host removal
  has already started or if reconnecting fails.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: David Dillow <dave@thedillows.org>
Cc: <stable@vger.kernel.org> # 3.8
Signed-off-by: Roland Dreier <roland@purestorage.com>