Rename to isTetheringFeatureEnabled

DeviceConfigUtils has isFeatureEnabled for NetworkStack and Tethering
which were confusing since the difference was only the arguments.
This CL renames isFeatureEnabled for Tethering module to
isTetheringFeatureEnabled to avoid confusion.

Bug: 279108992
Test: m
Change-Id: I05255bb38619afbe621d29524d7910d206a149f1
3 files changed