export_netdevs will export a net device for every port. These netdev represent a port
with out traffic.
When such a device is broght down via ifconfig the port is shutdown and
vice versa. Carrier sense is working too and ethtool can be used to
control advertise, autoneg, ...
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Backport of r42457
git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42475 3c298f89-4303-0410-b956-a3cf2f4a3e73