Update underlying networks if it is changed

It's possible that the VPN app updates its underlying networks
through Vpn#establish() instead of Vpn#setUnderlyingNetworks,
so establish() should also consider this case.

Bug: 191918368
Test: atest CtsHostsideNetworkTests:HostsideVpnTests
Change-Id: Iabcf0538121aeb839c6acfcc9b0005df5488a436

services/core/java/com/android/server/connectivity/Vpn.java

@@ -1398,7 +1398,10 @@ public class Vpn {
             // parameters. If that fails, disconnect.
             if (oldConfig != null
                     && updateLinkPropertiesInPlaceIfPossible(mNetworkAgent, oldConfig)) {
-                // Keep mNetworkAgent unchanged
+                // Update underlying networks if it is changed.
+                if (!Arrays.equals(oldConfig.underlyingNetworks, config.underlyingNetworks)) {
+                    setUnderlyingNetworks(config.underlyingNetworks);
+                }
             } else {
                 // Initialize the state for a new agent, while keeping the old one connected
                 // in case this new connection fails.