Allow module-bluetooth-device to listens to HandsfreeGateway state
changes using DBUS signals. When an handsfree connects, module-bluetooth-device
is loaded and goes to playing state. When the handsfree disconnect audio,
the card profile is set to "off". If the headset connects audio again after
that, the card profile should switch to "hfgw" again to match state of audio
connection.
It's perfectly normal for BlueZ to disable some endpoint types, so printing a
log message at error level isn't a good idea.
For facilitating an informative message in case some endpoint type is disabled,
the send_and_add_to_pending() function interface is also changed to be more
generic (the pa_bluetooth_device pointer is replaced with a void pointer).
NREC stands for Noise Reduction and Echo Cancelation, it can be changed
at any point by the headset.
When set to "1" indicates that those algorithms shall be enabled by
default and "0" means the headset probably have them active so they
should be disabled in PA side.
Acquire now return input and output MTU of the file descriptor so it is
no longer necessary to get those after acquiring the fd, which less round
trips and faster response time when switching profiles.
Create the 'Handsfree Gateway' profile for bluetooth cards and add
filters for 'org.bluez.HandsfreeGateway' to the discover module so
module-bluetooth-device is loaded with the correct profile when a
Handsfree Gateway connects to bluetoothd (in this case bluetoothd
is acting as the headset).
