urndis(4): retrospective, address for hselasky

PR: 273530
Fixes: 08c9016bc61b Add a manpage for the urndis driver.
Signed-off-by: Graham Perrin <grahamperrin@gmail.com>
Reviewed-by: imp, zlei
Pull-request: https://github.com/freebsd/freebsd-src/pull/834