GitLab

Some devices (e.g., ath79 MikroTik) have their MAC addresses configured
via /etc/config/network in "Xan_ethN_dev" device sections (e.g.,
lan_eth0_dev"). When removing old network settings, to not remove MAC
address settings.

Fixes #485.
Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>