Handle listening on duplicate addresses

Save listening address into listener. Use it to find existing listeners
before creating new one. If it exist, increase just used counter.
Release only listeners not already used.

Duplicates family in listener.

src/dnsmasq.h

@@ -572,7 +572,8 @@ struct irec {
 };
 
 struct listener {
-  int fd, tcpfd, tftpfd, family;
+  int fd, tcpfd, tftpfd, family, used;
+  union mysockaddr addr;
   struct irec *iface; /* only sometimes valid for non-wildcard */
   struct listener *next;
 };