This CL updates TestNetworkService to fully setup test TUN
interfaces when created. Previously, the interface was only
created in netd when the Test Network was created.
Bug: 182291467
Bug: 189125789
Test: atest Ikev2VpnTest IpSecManagerTunnelTest
Change-Id: I4c1262e566517bbb03dd610f595e4d18bc4e7735
Merged-In: I4c1262e566517bbb03dd610f595e4d18bc4e7735
(cherry picked from commit 615237a818)