NetworkPolicy: Validate policy templates before updating

Ensure all the policies to be added are validated, otherwise
this service will throw IllegalArgumentException and cause
system crash when updating network template after receiving
ACTION_NETWORK_STATS_UPDATED.

Change-Id: I3faef0ac2a2fcea64ba5dde9c9256f6714280e2e
CRs-Fixed: 561490
Merge "NetworkPolicy: Validate policy templates before updating" into du44