Enhance --domain to accept, interface names for the address range.

This allows hosts get a domain which relects the interface they
are attached to in a way which doesn't require hard-coding addresses.

Thanks to Sten Spans for the idea.

src/dnsmasq.h

@@ -975,6 +975,8 @@ struct dhcp_bridge {
 
 struct cond_domain {
   char *domain, *prefix; /* prefix is text-prefix on domain name */
+  char *interface;       /* These two set when domain comes from interface. */
+  struct addrlist *al;
   struct in_addr start, end;
   struct in6_addr start6, end6;
   int is6, indexed, prefixlen;