nameserv: return at most 16 addresses from DNS_Name2IPAddress()

This is the same limit as in the asynchronous resolver. Use common macro
for all buffers storing IP addresses.

nameserv.h

@@ -39,6 +39,9 @@ typedef enum {
 /* Resolve names only to selected address family */
 extern void DNS_SetAddressFamily(int family);
 
+/* Maximum number of addresses returned by DNS_Name2IPAddress */
+#define DNS_MAX_ADDRESSES 16
+
 extern DNS_Status DNS_Name2IPAddress(const char *name, IPAddr *ip_addrs, int max_addrs);
 
 extern int DNS_IPAddress2Name(IPAddr *ip_addr, char *name, int len);