bluez5: delay SCO transport releases in case they get reacquired

SCO socket connect may fail with ECONNABORTED if it is done too soon
after previous close. To avoid this in cases where nodes are toggled
between stopped/started rapidly, postpone release until the transport
has remained unused for a time. Since this behavior appears common to
multiple SCO backends, do it for all SCO backends.

spa/plugins/bluez5/defs.h

@@ -300,6 +300,8 @@ struct spa_bt_transport {
 	void *user_data;
 	struct spa_bt_sco_io *sco_io;
 
+	struct spa_source release_timer;
+
 	struct spa_hook_list listener_list;
 	struct spa_callbacks impl;
 };