[PATCH] Close SCO before headset interface state change

Hi,

Attached is a tentative patch proposal, I'm not sure how to make this
modification in a good way.

Maybe the check for G_IO_NVAL in sco_cb should not be removed, but
that is the GIOCondition the callback receives
when shutting down the SCO socket.
It was added in commit
http://git.kernel.org/?p=bluetooth/bluez.git;a=commit;h=6834de18b98fea0e7d370a296318115a659047af

Br,
Daniel