device: Fix invalid read in att_connect_cb
device: Fix invalid read in att_connect_cb

We should keep a reference to GIOChannel created in att_connect so we
can properly shut it down if the device is removed during a connection
attempt. After establishing the connection, we drop the GIOChannel
reference because GAttrib will take the responsability of disconnect the
link based on the registered ATTIO connection callbacks.

This patch fixes the following invalid read reported by valgrind when
the device is removed and we have a ongoing connection attempt:

Invalid read of size 4
   at 0x1A90D8: att_connect_cb (device.c:1712)
   by 0x17EDB9: connect_cb (btio.c:169)
   by 0x4E6E29C: g_main_context_dispatch (in /usr/lib/libglib-2.0.so.0.2800.8)
   by 0x4E6EA77: ??? (in /usr/lib/libglib-2.0.so.0.2800.8)
   by 0x4E6F0B9: g_main_loop_run (in /usr/lib/libglib-2.0.so.0.2800.8)
   by 0x18ACB3: main (main.c:485)
 Address 0x68aacb8 is 456 bytes inside a block of size 472 free'd
   at 0x4C2556E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x1A596B: device_free (device.c:248)
   by 0x121EB5: remove_interface (object.c:563)
   by 0x122288: g_dbus_unregister_interface (object.c:715)
   by 0x1AAFD8: btd_device_unref (device.c:2636)
   by 0x1A7912: device_remove (device.c:1058)
   by 0x19F371: adapter_remove_device (adapter.c:1122)
   by 0x1A0AD4: remove_device (adapter.c:1720)
   by 0x1214C4: process_message (object.c:224)
   by 0x121B60: generic_message (object.c:447)
   by 0x51348C0: ??? (in /usr/lib/libdbus-1.so.3.5.7)
   by 0x512679F: dbus_connection_dispatch (in /usr/lib/libdbus-1.so.3.5.7)

silent-snowman/bluez,ComputeCycles/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,ComputeCycles/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,ComputeCycles/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,mapfau/bluez