Tidy uid defines.

src/cache.c

@@ -298,7 +298,7 @@ struct crec *cache_enumerate(int init)
 
 static int is_outdated_cname_pointer(struct crec *crecp)
 {
-  if (!(crecp->flags & F_CNAME) || crecp->addr.cname.uid == 0)
+  if (!(crecp->flags & F_CNAME) || crecp->addr.cname.uid == SRC_INTERFACE)
     return 0;
   
   /* NB. record may be reused as DS or DNSKEY, where uid is 

src/rfc1035.c

@@ -2018,7 +2018,7 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
 			    
 			    strcpy(name, cname_target);
 			    /* check if target interface_name */
-			    if (crecp->addr.cname.uid == 0)
+			    if (crecp->addr.cname.uid == SRC_INTERFACE)
 			      goto intname_restart;
 			    else
 			      goto cname_restart;