RDS: make send_batch_count tunable effective

RDS: make send_batch_count tunable effective

The send_batch_count tunable is stale and code relies on
hard-coded batch count value. Its a nice feature and lets you
tune the system based on different HCAs. TCP transport as well
have different characteristics and tunable can be useful.

There is no change in default behavior with this patch.

Orabug: 22010933

Acked-by: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Acked-by: Wengang Wang <wen.gang.wang@oracle.com>
Reported-by: Wei Lin Guay <wei.lin.guay@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>