flags: Add fix_nonconnectable_scannable_advertisement

Add fix_nonconnectable_scannable_advertisement flag,
which will be used to put the fix for b/312883465
behind a flag.

Bug: 316013235
Bug: 312883465
Test: m service-bluetooth
Change-Id: I6ce907fa25aa48f3d2ca2b06e6f2049fc81e6760