Dump mNetworkToIfaces in NetworkPolicyManagerService

Dump last interfaces of the network information in dumpsys of
netpolicy.

Output:
Network to interfaces:
  100: {rmnet_data1}]
  101: {v4-wlan0, wlan0}]

Bug: 237640200
Test: FrameworksNetTests
Change-Id: I258f5565e62666cd71222073c692e45e2e5828e2