Allow system components to request underlying network policies.

This CL updates VcnManager to allow system components with permission
NETWORK_FACTORY to request the current VcnUnderlingNetworkPolicy for a
specific Network's NetworkCapabilities and LinkProperties.

Bug: 175900686
Test: atest FrameworksVcnTests
Change-Id: I16416e619bdb03630582f5660260b0090730e9eb
5 files changed