rds: avoid call to flush_mrs() in specific condition

rds: avoid call to flush_mrs() in specific condition

This is to reduce process spawn time.
When user provides 0 values for cookie and flags in rds_free_mr() call,
avoid calling flush_mr()

skgxp uses cookie 0 and flag 0 combination for checking whether
transport is RDMA capable or not.

This is short term hack for customer escalation.
Customer is having other processes which are calling flush_mrs() and
that is causing mutex contention.
skgxp change is fairly significant, and we want to provide minimal
change in customer environment.

Risk factor here is, if there is any other use of cookie 0 and flag 0
combination (like freeing up unused MRs), then that will be impacted.
Code inspection by Leo/Avneesh at skgxp and skgnfs suggests that, this
combination not being used anywhere.

Long term solution for this requires changes in RDS as well as skgxp
application, which should be done in next UEK release.
Required RDS changes are present in UEK4; however, skgxp changes are
still remaining. Since this was escalation from major customer, we
require this hack in UEK4.

Orabug: 24656750

Tested-by: Sujatha Tolstoy <sujatha.tolstoy@oracle.com>
Signed-off-by: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Reviewed-by: Leo Tominna <leo.tominna@oracle.com>
Reviewed-by: Avneesh Pant <avneesh.pant@oracle.com>
Reviewed-by: John Sobecki <john.sobecki@oracle.com>
Signed-off-by: Guangyu Sun <guangyu.sun@oracle.com>