interface: add neighbor config support

interface: add neighbor config support

The neighbor or neighbor6 network section makes neighbours
configurable via UCI or proto shell handlers. It allows to
install neighbor proxy entries or static neighbor entries

The neighbor or neighbor6 section has the following types:
	interface : declares the logical OpenWrt interface
	ipaddr : the ip address of the neighbor
	mac : the mac address of the neighbor
	proxy : specifies whether the neighbor ia a proxy
		entry (can be 1 or 0)
	router : specifies whether the neighbor is a router
		 (can be 1 or 0)

Signed-off-by: Alexander Meuris <meurisalexander@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>