Fix projects without PPP do not compile any more

src/core/init.c

@@ -60,6 +60,8 @@
 #include "lwip/mld6.h"
 #include "lwip/api.h"
 
+#include "netif/ppp/ppp_opts.h"
+
 /* Compile-time sanity checks for configuration errors.
  * These can be done independently of LWIP_DEBUG, without penalty.
  */

src/include/lwip/memp.h

@@ -33,6 +33,9 @@
 #ifndef LWIP_HDR_MEMP_H
 #define LWIP_HDR_MEMP_H
 
+/* needed by memp_std.h */
+#include "netif/ppp/ppp_opts.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif