[net] rename js_etherif -> js_netif. doesn't compile yet
[net] js_etherif->js_netif - remove etherif specific functions
[net] js_etherif->js_netif - API change
[net] use js_netif in js_linux_eth
[net] fix linux eth example
[net] adapt enc2860 and stellaris_eth JS bindings to use js_netif (and fix some descriptions on the way)