mpt3sas: Don't block the drive when drive addition under the control of SML

mpt3sas: Don't block the drive when drive addition under the control of SML

During hot-plugging of a disk(having a flaky link), the disk addition
stops and any further disk addition or removal doesn't happen on that
controller.

This is because, when driver receives DELAY_NOT_RESPONDING event for a disk
while it is undergoing addition at the SCSI Transport layer, the driver
would block the I/O to that disk resulting in a deadlock. i.e the disk
addition work couldn't be completed at the SCSI Transport Layer as it
can't send any I/Os (such as Inquiry, Report LUNs etc) to the disk as
I/Os are blocked to this drive. Also any subsequent device removal
(TARGET_NOT_RESPONDING) or link update(RC_PHY_CHANGED) event couldn't be
processed as they are in the queue to get processed after disk addition
event.

Description of Change:
Don't block the drive when drive addition is under the control of SML.
So that SML won't be blocked of issuing the device dicovery commands
(such as Inquiry, Report LUNs etc).

Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@avagotech.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>