Use LWIP_PLATFORM_DIAG for LWIP

fprintf() is not guaranteed to be available. Or even printf().

Signed-off-by: Vlad Lungu <vlad.lungu@windriver.com>

src/debug.c

@@ -34,6 +34,11 @@
 #include "encode.h"
 #include "net.h"
 
+#ifdef WITH_LWIP
+# define fprintf(fd, ...) LWIP_PLATFORM_DIAG((__VA_ARGS__))
+# define fflush(...)
+#endif
+
 #ifdef WITH_CONTIKI
 # ifndef DEBUG
 #  define DEBUG DEBUG_PRINT