In order to extend features based on provided features, we need to
check contents of `FEATURES_PROVIDED`.

If a board already provided a netif_% feature (currently only
netif_ethernet), the netif feature is automagically provided.

Use periph_eth instead of esp_eth for the Ethernet peripheral on ESP
MCUs for consistency

If there is an Ethernet peripheral (periph_eth feature provided), we
can conclude that an Ethernet network interface can be provided.

Co-authored-by: mguetschow <mikolai.guetschow@tu-dresden.de>