Revert "handsfree-audio: Reject .Connect() from other senders"

This reverts commit 31285737417aa8a2bb0b832a43d115cdcc397751.
emulator: Change feature check to attend HFP 1.6
emulator: Add Handsfree Audio Card to emulator
emulator: Remove Audio Card when destroy emulator
emulator: Register card when SLC is established
hfp_ag: Add emulator to modem when connect
hfp_ag: Remove emulator from modem when disconnect
hfp_ag: Add Audio Card to emulator when connect
hfp_ag: Set Audio Card's local and remote address
hfp_ag: Add a card driver for HFP 1.6

This is just the skeleton of a Handsfree Audio Card for the HF side of
HFP 1.6.
hfp_ag: Extract Version from fd dictionary
hfp_ag: Pass version to card registration
hfp_ag: Register BCC callback handler

This commit registers a callback to be executed when the HFP AG 1.6
receives a AT+BCC command.