Expose lwIP's DNS API in zts_* API. Fix preprocessor build bug

src/lwipopts.h

@@ -1199,7 +1199,7 @@ happening sooner than they should.
  * transport.
  */
 #if !defined LWIP_DNS || defined __DOXYGEN__
-#define LWIP_DNS                        0
+#define LWIP_DNS                        1
 #endif
 
 /** DNS maximum number of entries to maintain locally. */
@@ -1710,7 +1710,7 @@ happening sooner than they should.
 #endif
 
 /**
- * LWIP_NETIF_EXT_STATUS_CALLBACK==1: Support an extended callback function 
+ * LWIP_NETIF_EXT_STATUS_CALLBACK==1: Support an extended callback function
  * for several netif related event that supports multiple subscribers.
  * @see netif_ext_status_callback
  */
@@ -2324,7 +2324,7 @@ happening sooner than they should.
  * All addresses that have a scope according to the default policy (link-local
  * unicast addresses, interface-local and link-local multicast addresses) should
  * now have a zone set on them before being passed to the core API, although
- * lwIP will currently attempt to select a zone on the caller's behalf when 
+ * lwIP will currently attempt to select a zone on the caller's behalf when
  * necessary. Applications that directly assign IPv6 addresses to interfaces
  * (which is NOT recommended) must now ensure that link-local addresses carry
  * the netif's zone. See the new ip6_zone.h header file for more information and
@@ -2962,8 +2962,8 @@ happening sooner than they should.
  * - src: source eth address
  * - dst: destination eth address
  * - eth_type: ethernet type to packet to be sent\n
- * 
- * 
+ *
+ *
  * Return values:
  * - <0: Packet shall not contain VLAN header.
  * - 0 <= return value <= 0xFFFF: Packet shall contain VLAN header. Return value is prio_vid in host byte order.
@@ -3451,4 +3451,4 @@ happening sooner than they should.
  * @}
  */
 
-#endif /* LWIP_HDR_OPT_H */
+#endif /* LWIP_HDR_OPT_H */