Add VCN CTS to mts-tethering

This patch adds CtsVcnTests to tethering MTS. Consequently,
these tests will be monthly updated and installed with Tethering
module on all Android R/R+ devices. Thus the patch also adds
SDK checks to make sure the mainline updated tests will be skipped
if SDK <= Android V, to avoid compatability issues.

Bug: 376896491
Test: lunch mainline_modules_arm64-mainline-userdebug &&
      m mts && mts-tradefed run mts-tethering;
      Verified on V and B
Flag: EXEMPT; test code change
Change-Id: Ib6d3d698925feef472d472be6def080580aa6ec3