Notify PolicyListeners to refresh their policy on VCN changes.

This CL updates VcnManagementService to notify all registered
VcnUnderlyingNetworkPolicyListeners to refresh their
UnderlyingNetworkPolicy when any VCN is added or removed.

Bug: 175914059
Test: atest FrameworksVcnTests
Change-Id: Ie87f4aa3401c6c4ba9f932130a1d475e35f59d4e
2 files changed