Remove Protocol.BASE_* usage in Connectivity

ConnectivityManager and NetworkAgent do not share their handler with any
other component, so there is no reason to use addresses that do not
overlap. Protocol.BASE_* was written to allow for interaction "between
different StateMachine implementations without a conflict", but the
classes do not use StateMachine, and they do not have such interactions.

Bug: 177046265
Test: atest FrameworksNetTests
Change-Id: I18c341d4a2c01cb9559d682a9ad1ff259e6b5855