Revert "Revert "Share radio settings across interfaces.""

Fixes the root cause of b/34130314, which caused the initial
reversion.  Also adds unit test coverage for the code which contained
the bug.

BUG=34130314,31074359

This reverts commit 5c7908d5e28fcd875b1e280280f2894910bd23a7.

Change-Id: I61173ba1147de23fe89833e895eb26f88e53125a
5 files changed