Conditionally disable TetheringApiCurrentLib

The "current" targets are only necessary in branches that can use
non-stable APIs, and can fail to build otherwise.

Apply ConnectivityNextEnableDefaults so they are disabled on such
branches. Also deprecate NetworkStackNextEnableDefaults, so
ConnectivityNextEnableDefaults is used everywhere.

Bug: 190249673
Test: m
Change-Id: I1b152f3cc22f1bed6444d280f0066e480980e949
2 files changed