Put sdk_version in module stub defaults

Makes it easier to change when every module isn't specifying
how the stubs are built.

Also make wifi stubs build against the appropriate api surface, which
works around a bug.

Bug: 147768409
Bug: 151134996
Test: m
Change-Id: I91db06ef932a73002b4fe232566f5d111baef432
Merged-In: I91db06ef932a73002b4fe232566f5d111baef432