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

services/core/java/com/android/server/net/NetworkPolicyManagerService.java

@@ -4049,6 +4049,14 @@ public class NetworkPolicyManagerService extends INetworkPolicyManager.Stub {
                 }
                 fout.decreaseIndent();
 
+                fout.println("Network to interfaces:");
+                fout.increaseIndent();
+                for (int i = 0; i < mNetworkToIfaces.size(); ++i) {
+                    final int key = mNetworkToIfaces.keyAt(i);
+                    fout.println(key + ": " + mNetworkToIfaces.get(key));
+                }
+                fout.decreaseIndent();
+
                 fout.println();
                 mStatLogger.dump(fout);