emulator: Add AT+BAC support

When the emulator receives a AT+BAC SET command, it stores the
available HF codecs.
emulator: Setup codec connection

This commit sends an unsolicited +BCS command with the selected codec
after the AG receives a AT+BAC command.

If the service level connection isn't established, postpone the +BCS
to after the establishment.

Currently the codec is hardcoded to CVSD.
emulator: Receive AT+BCS response

This commit verifies the codec sent by HF and, if it is valid, set it
in the Handsfree Audio Card.
emulator: Resend +BCS after receive AT+BAC

If the AG receives AT+BAC as a response to an unsolicited +BCS, it
will resend +BCS based on the new list of available codecs.
emulator: Add AT+BCC support

This commit setups a synchronous connection when AG receives a AT+BCC
command.
emulator: Add Codec Negotiation feature

This commit adds Codec Negotiation to the list of AG features
supported by the emulator.
TEMP: Don't check Card.Connect() D-Bus sender
WIP: test: Add hfp-answer-call-with-sco