The version of GVC used by GSD is missing the latest commit upstream that fixes a problem in gnome-control-center related to duplicated output devices showing up in GCC's sound panel(see [1]), which in principle is not needed for the shell.

However, I found locally that that fix actually makes a difference in the shell as well when connecting a Bluetooth device from the shell's top panel, in that an unnecessary call to match_card_port_with_existing_device() is being executed due to the (card_port->available != info->ports[i]->available) condition being not good enough, as it does not take UNKNOWN availability into account.

So, as this is a small change anyway (only this commit was missing from shell's gvc submodule), I'm proposing to update it there too in the same way it was done already for the other modules bundling GVC (g-s-d and g-c-c).

[1] https://git.gnome.org/browse/libgnome-volume-control/commit/?id=fac3a900e5de2c60d667c54f2727e806d29cff4b