Add '-unstable' to solve ODR violation

The interface which is imported by an unstable interface is 'unstable'
as well. Until now, the ODR violation checker in aidl has omitted an
interface imported, but it will be checked, accordingly, fix the current
problem

Bug: 146436251
Test: m nothing
Change-Id: Id3c4bbc9149ba7c3e0a0d728026f02f60cb17424
Merged-In: Id3c4bbc9149ba7c3e0a0d728026f02f60cb17424
Exempt-From-Owner-Approval: cp from internal