Rename Bluetooth stack function parameters to clearly indicate what sort of Bluetooth channel (ACL, RFCOMM) is required for each parameter, to make the code easier to read.

Add a new RFCOMM_ChannelSignalsReceived() Bluetooth stack callback from the RFCOMM layer for when the remote device sends new terminal control signals.

Fix RFCOMM_SendData() not aborting correctly when the requested RFCOMM channel is not found.