When workspaces-only-on-primary is set and a window is moved back to the
primary, we also move it to the active workspace to avoid the confusion
of a visible window suddenly disappearing when crossing the monitor border.
However when the window is not actually moved by the user, preserving the
workspace makes more sense - we already do this in some cases (e.g. when
moving between primary monitors), but miss others (unplugging the previous
monitor); just add an explicit user_op parameter as used elsewhere to cover
all exceptions.

https://bugzilla.gnome.org/show_bug.cgi?id=731760