This adds Acquire method which can be used by agents that require
pulling the fd directly instead of waiting a NewConnection.
Note: sounds servers like PulseAudio do auto suspend streams when idle
for a certain amount of time and once anything happens it will resume
the stream, though this all happens in the so called IO thread in a
blocking fashion making it impossible to receive the fd via NewConnetion
causing the stream to fail to resume. There are other forms to work
around but this seems to be most convenient as we do want the auto
suspend feature to work properly but letting the stream to fail to
resume may create unexpected artifacts while the NewConnection is
handled in main thread.
When registering audio cards for the handsfree and gateway roles we
need a way for our users to differentiate between both to decide which
of them they start using for their purpose.
Luiz Augusto von Dentz
Simon Fels
Claudio Takahasi
Denis Kenzior