Bluetooth: Fix startAdvertisingSet error handling

Calls to old advertising API (startAdvertising), should never throw
exceptions. Instead, it used to post failure callback. This behaviour
was accidentally modified when implementing new API. Right now, instead
of posting error callback, we throw IllegalArgumentException if we fail
to obtain BluetoothGatt object, or the call to startAdvertisingSet
fails.

This patch brings back the old behaviour to the API. It also makes new
API post callback instead of throwing exception in this error case.

Bug: 63819108
Test: manual
Change-Id: I897b99839f899ca3f3dc609918d665c8c327b777
Merged-In: I897b99839f899ca3f3dc609918d665c8c327b777
(cherry picked from commit f7bd6b26)