scsi: lpfc: Fix MDS diagnostics failure (Rx < Tx)

MDS diagnostics fail because of frame count mismatch.

Unavailability of SGL is the trigger for this issue. If ELS SGL is not
available to process MDS frame, IOCB is put in FCP txq but not attempted to
post afterwards. So, driver stops processing incoming frames as it runs out
of IOCB.  lpfc_drain_txq attempts to submit IOCBS that are queued in ELS
txq but MDS frames are posted to FCP WQ.

Attempt to submit IOCBs that are present in FCP txq when MDS loopback is
running.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>