status/network: Also show disabled icon when wwan is not connected

Commit ca4f6e01 was supposed to show the
"cellular-disabled" icon when wwan is disabled. For wwan, just like for
bluetooth wwan networks, we probably want this to include the "not
connected" state, because disconnecting from cellular service de-facto
means disabling it.

So switch the check to show the "cellular-disabled" icon to also use the
icon whether there's no active connection, not only when the wwan device
is turned off.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5401

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2283>