Mock permission checks for NetworkManagementServiceTest

NetworkManagementService has been migrated to use AIDL annotations for
permission enforcement. Mock the PermissionEnforcer to ensure the
control of which permission are checked. Pass down the current
PermissionEnforcer to the parent Stub class via the constructor.

Bug: 259341026
Test: atest FrameworksServicesTests:com.android.server.NetworkManagementServiceTest
Change-Id: I83aabf22cbf0d34a683c51f3d09110fbd5daae6d