api_msg.c, dns.h, dns.c: Implement DNS_DOES_NAME_CHECK option (check if name received match the name query), implement DNS_USES_STATIC_BUF (the place where copy dns payload to parse the response), return an error if there is no place for a new query, and fix some minor problems.

src/include/lwip/dns.h

@@ -81,6 +81,7 @@
 
 /* enumerated list of possible result values returned by dns_gethostname() */
 typedef enum dns_result {
+  DNS_ERR_MEM,
   DNS_QUERY_INVALID,
   DNS_QUERY_QUEUED,
   DNS_COMPLETE