istio: fix PILOT_ENABLE_RDS_CACHE flag not working (#40719)
istio: fix PILOT_ENABLE_RDS_CACHE flag not working (#40719)

When building RDS, cache get is always conducted not respecting the
PILOT_ENABLE_RDS_CACHE flag. This CL fixes that.

Cache add already respects the flag:
https://github.com/airbnb/istio/blob/1.14.3-airbnb1/pilot/pkg/networking/core/v1alpha3/httproute.go#L212

Change-Id: Ic0634647239a6def8ced4ce611f5a986f130c95a
Reviewed-on: https://gerrit.musta.ch/c/public/istio/+/3611
Reviewed-by: Douglas Jordan <2164e60b3f173daab940463ad3b52c3974674ead@airbnb.com>
Reviewed-by: Jungho Ahn <c96f69c8fb2276b7d299d75aa6aae561ce117dee@airbnb.com>
Reviewed-by: Weibo He <d4e8291c3dbcb0f3ba5830898652c1c12ab9fa13@airbnb.com>
istio/istio,istio/istio,istio/istio,istio/istio,istio/istio