Do not depend on Tethering stubs in CM consts

Tethering API stubs depend on connectivity stubs for classes like
MacAddress or LinkAddress, so connectivity stubs cannot depend on
Tethering stubs or there would be a circular dependency.

This means ConnectivityManager API surface cannot reference Tethering
API constants. Instead, use the literal in ConnectivityManager.

This means that both ConnectivityManager and TetheringManager specify
the constant value. An alternative considered was to have
TetheringManager depend on the ConnectivityManager constants, but
considering that ConnectivityManager only has some of the constants,
this would be more confusing. Breaking the constants by mistake is
unlikely as their values are part of the API surface, so will always be
in sync.

Bug: 171540887
Test: m
Change-Id: I16b6e1912fffc5ff8b3b392901d2357ffd213c72