[BPI-R2] Ubuntu 18.4 with kernel 4.14.48

[frank-w]

iface et inet static

if you use kernel 4.14+ you have to set ip on dsa-interface (lanx,wan) and only bring ethx up

example for lan0:

https://www.fw-web.de/dokuwiki/doku.php?id=en/bpi-r2/network/start#permanent