ofono.conf: Punch hole for HandsfreeAudioAgent
handsfree-audio: Add support for initiating SCO connections

When calling the card's .Connect() method, we should be able to
establish a SCO connection.

Right now, we only have support for establishing the SCO connection
directly, this is what is expected from HFP 1.5 HF/AG devices.
handsfree-audio: Add support for sending the SCO socket

Send the SCO socket to the agent associated with the card that
just got connected.
handsfree-audio: Reject .Connect() from other senders

Only the agent should be able to call .Connect() on the card.
doc: Add Handsfree Audio Card "Connect" errors
hfp_hf_bluez5: 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: Add Handsfree Audio Card to emulator
hfp_ag: Create/remove Audio Card in emulator
hfp_ag: Set card's local and remote address
hfp_ag: Register card when SLC is established
hfp_ag: Remove card when disconnect HFP AG profile
emulator: Change feature check to attend HFP 1.6
Revert "handsfree-audio: Reject .Connect() from other senders"

This reverts commit 32d18976879bbc93da811ab88eade4e98bb248fa.