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
1 file changed