xwayland: Only prevent focus change to inactive toplevels

Commit b18f788e2e76 broke motif applications by ensuring they could never
focus their menus - since then any attempt by an application to focus any
window would be met by the window manager immediately refocusing the
currently active toplevel window.

Later we loosened the restriction in 9e07d25a to allow clients that
received focus from a grab to do so - but motif applications like nedit
don't set focus in this way, and remain broken.

This patch further loosens our restrictions, now only reverting a focus
change to an inactive top level. This will hopefully prevent any
confusing input routing without breaking reasonable clients.

This restores functionality to motif menus.

Fixes #636
Fixes b18f788e

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>