Mock Vpn.setUnderlyingNetworks()

Override Vpn.setUnderlyingNetworks() to do a direct call on the
network agent instead of relying on the Vpn class.

Bug: 230548427
Test: atest FrameworksNetTests
Change-Id: Ib7883f8a81a22317616cae79ce57a30afdd2bed4
1 file changed