l2cap: Notify upper layer about credit based conn request collision

When Android handles local Credit Based Connection request, the
incoming requests are rejected. With this patch, upper layer will know
about collision and can handle it later on if needed

Bug: 236216322
Test: atest BluetoothInstrumentationTests
Test: PTS
Tag: #stability
Change-Id: Iebaee7ecfa4b1c330fd42e5755d5e43b6a334aab