coap_net.h: add ifdef WITH_LWIP around lwip functions

doc/Doxyfile.in

@@ -2210,7 +2210,7 @@ INCLUDE_FILE_PATTERNS  =
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = @PREDEFINED_CFLAGS@
+PREDEFINED             = @PREDEFINED_CFLAGS@ __DOXYGEN__
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The

include/coap3/coap_net.h

@@ -803,6 +803,7 @@ COAP_API void coap_io_do_epoll(coap_context_t *ctx, struct epoll_event *events,
 
 /**@}*/
 
+#if defined(WITH_LWIP) || defined(WITH_LWIP_MAN_CHECK) || defined(__DOXYGEN__)
 /**
  * @ingroup application_api
  * @defgroup lwip LwIP specific API
@@ -848,6 +849,7 @@ void coap_lwip_set_input_wait_handler(coap_context_t *context,
                                       void *input_arg);
 
 /**@}*/
+#endif /* WITH_LWIP || WITH_LWIP_MAN_CHECK || defined(__DOXYGEN__) */
 
 /**
  * @deprecated Use coap_io_process() instead.

man/examples-code-check.c

@@ -168,6 +168,9 @@ check_synopsis(const char *file) {
     exit_code = 1;
     return;
   }
+  if (!strcmp(file, "coap_lwip.txt.in")) {
+    fprintf(fpcode, "#define WITH_LWIP_MAN_CHECK\n");
+  }
   fprintf(fpcode, "#include <coap3/coap.h>\n");
   fprintf(fpcode, "#ifdef __GNUC__\n");
   fprintf(fpcode, "#define U __attribute__ ((unused))\n");