net/mpd5: install dictionary.mpd and add fix r2441 from upstream

* Add dictionary.mpd to default package build and install it
to /usr/local/share/mpd/dictionary.mpd.

Thanks Dmitry Luhtionov who noted this omission.

* If parent interface of PPPoE link (vlan, detachable USB ethernet etc.)
got destroyed and re-added, detect that and continue automatically;
manual interference was required before this import of upstream r2441.