http_client.c: Fix compile when TCP is disabled

src/apps/http/http_client.c

@@ -57,6 +57,8 @@
 #include <stdio.h>
 #include <string.h>
 
+#if LWIP_TCP && LWIP_CALLBACK_API
+
 /**
  * HTTPC_DEBUG: Enable debugging for HTTP client.
  */
@@ -902,3 +904,5 @@ httpc_get_file_dns_to_disk(const char* server_name, u16_t port, const char* uri,
   return ERR_OK;
 }
 #endif /* LWIP_HTTPC_HAVE_FILE_IO */
+
+#endif /* LWIP_TCP && LWIP_CALLBACK_API */

src/include/lwip/apps/http_client.h

@@ -45,6 +45,8 @@
 #include "lwip/prot/iana.h"
 #include "lwip/pbuf.h"
 
+#if LWIP_TCP && LWIP_CALLBACK_API
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -153,4 +155,6 @@ err_t httpc_get_file_dns_to_disk(const char* server_name, u16_t port, const char
 }
 #endif
 
+#endif /* LWIP_TCP && LWIP_CALLBACK_API */
+
 #endif /* LWIP_HDR_APPS_HTTP_CLIENT_H */