We considered any ConnectFlag value major than SWAPPED as invalid, while
it's technically not fully true as we need to ensure that the passed
value is respecting the whole flags mask.
In fact, per se SWAPPED|AFTER (> SWAPPED) is a valid value (even if we
don't support the AFTER value).
But this makes the check more future-proof.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2366>