Looks like this is new as of the 4.2 timeframe. It does bring up a
question: should we do a ls /proc/sys/net/conf/lo on the host to figure out
what sysctls to try and dump instead of use this hardcoded list? I guess we
need to check file modes too, because of mc_forwarding, but something like
that.

v2: add ignore_routes_with_linkdown to the end of the hardcoded devconfs
    list, so as not to break migration across criu versions.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>