Use a TAP test network for MeshCoP service test cases

Previously we were using TUN test network which is not eligible for mDNS
operations. The tests are flaky because we need to depend on other test
cases to connect to WiFi, which is not guaranteed. We'll use the TAP
test network to fix it.

Bug: 327306555
Bug: 327306158
Bug: 327306608

Change-Id: Ia6de8a507578dbdeea4a7ceaf52f417acf35baa2