Rewrite the manual page for wg(8) and remove
most of the Linuxism's. Since the manual page itself
is based on roff(7) rewrite it with mdoc(7) macros.
This is a direct commit to contrib and was discussed
with kevans@ before. Its planned to upstream this
manual page once it's landed.
Reported by: lwhsu, gbe
MFC after: 1 week