NPMS lock improvement.

Fix NPMS lock contention:
Between 'com.android.server.net.NetworkPolicyManagerService$NetworkPolicyManagerInternalImpl.isUidNetworkingBlocked(int, java.lang.String)' and 'com.android.server.net.NetworkPolicyManagerService$NetworkPolicyManagerInternalImpl.getSubscriptionPlan(android.net.NetworkTemplate) on lock mNetworkPoliciesSecondLock.

Bug: 162350812
Test: regresstion test.
Change-Id: Ibbb4325c7380a2febf3682b3ae3436647ae82e16
Merged-In: Ibbb4325c7380a2febf3682b3ae3436647ae82e16