While OpenResolv supports explicit ordering directives such as `-m` and
exclusivity directives such as `-x`, Debian's own resolvconf supports
none of this, instead using a hard coded list of interface name
templates for determining ordering. While trying to emulate `-x` is
difficult [*], we can at least try to mostly emulate `-m 0` by
masquerading as a `tun*` interface to resolvconf. Ugly, but it works.
[*] One heavy handed way of emulating `-x` would be something like:
# echo nameserver 8.8.8.8 > /etc/resolv.conf.wg0-exclusive
# mount --bind -o ro /etc/resolv.conf.wg0-exclusive /etc/resolv.conf
# rm -f /etc/resolv.conf.wg0-exclusive
This in practice works quite well, but is a bit heavy to put in a man
page. It also doesn't "stack" well. For example, if we simply run
`umount /etc/resolv.conf`, how do we know which resolv.conf entry we're
unmounting?
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>