Initial entry for L2CAP data pipeline and cert

* Attach data channel to scheduler
* Enable page scan on L2CAP module start
* Add test for L2CAP classic fixed channel connection and data
* Fix GetQueueUpEnd() API for Fixed Channel

Bug: 138261142
Test: cert/run_cert.sh
Change-Id: Ic3035546933a9ad08712e757c65d8455b09dd36a