Revert "[SCSI] libiscsi: Reduce locking contention in fast path"

Revert "[SCSI] libiscsi: Reduce locking contention in fast path"

Orabug: 25975223

This reverts commit 659743b02c411075b26601725947b21df0bb29c8.

Conflicts:
	drivers/scsi/be2iscsi/be_main.c
	drivers/scsi/bnx2i/bnx2i_iscsi.c
	drivers/scsi/iscsi_tcp.c
	drivers/scsi/libiscsi.c
	drivers/scsi/be2iscsi/be_main.c

659743b02c41 splits iscsi session lock into two locks, one to be used while
sending a request to the target and the other to be used while processing
a response. This patch has caused multiple bugs due to races while
accessing various lists that hold the iscsi_task in the iscsi_conn
structure.

Although commit 6f8830f5bbab in upstream partially fixes the issue, there
is still atleast one regression seen when the same iscsi task is accessed
simultaneously in iscsi_xmit_task() and iscsi_complete_task() which causes
a null pointer dereference and panic.

Its best to revert this patch until we find a permanent solution.

Signed-off-by: Ashish Samant <ashish.samant@oracle.com>
Reviewed-by: John Sobecki <john.sobecki@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>