BLE Advertising Manager test improvements

This patch moves mock verification before call to callback. If for any
reason the callback is not properly initialized, this is usually due to
fact that the call didn't reach the mock. Right now in such cases we get
a crash and stack trace. After this patch we will first get information
about the mock not being called properly, then the crash, which would
make debugging such issues much easier.

Bug: 30622771
Test: manual test
Change-Id: Ia182f2eed384924395e8d6b6a2d3d0abd393a4ee