RDS: IB: disable ib_cache purging to avoid memory leak in reconnect path

RDS: IB: disable ib_cache purging to avoid memory leak in reconnect path

RDS IB caches don't work in reconnect path and if used can lead to
memory leaks. These leaks have been there for long time but we didn't
hit them since caches are not teardown in reconnect path. For different
frag rolling upgrade/downgrade support, its needed to work in reconnect
path but needs additional fixes.

Since the leak is blocking rest of the testing, temporary the cache
purging is disabled. It will be added back once fully fixed.

Orabug: 23275911

The change doesn't impact any of the existing RDS functionality.

Tested-by: Hong Liu <hong.x.liu@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>