Adds support in uci for configuring multiple dnsmasq instances via
multiple dnsmasq sections.
The uci sections host, boot, mac, tag, vendorclass, userclass,
circuitid, ... will refer to a dnsmasq instance via the instance
parameter defined in the section; if the instance parameter is
not specified backwards compatibility is preserved.
Start/Stopping a dnsmasq instance can be achieved by passing the
dnsmasq instance name as argument to start/stop via the init script.
Multiple dnsmasq instances is usefull in scenarios where you want to
bind a dnsmasq instance to an interface in order to isolate networks.
This patch is a rework of a multiple dnsmasq instance patch by Daniel Dickinson
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>