minor: corrected include guard name in tcp_priv.h
diff --git a/src/include/lwip/priv/tcp_priv.h b/src/include/lwip/priv/tcp_priv.h
index 51747e0..f0eeb45 100644
--- a/src/include/lwip/priv/tcp_priv.h
+++ b/src/include/lwip/priv/tcp_priv.h
@@ -34,8 +34,8 @@
  * Author: Adam Dunkels <adam@sics.se>
  *
  */
-#ifndef LWIP_HDR_TCP_IMPL_H
-#define LWIP_HDR_TCP_IMPL_H
+#ifndef LWIP_HDR_TCP_PRIV_H
+#define LWIP_HDR_TCP_PRIV_H
 
 #include "lwip/opt.h"
 
@@ -501,4 +501,4 @@
 
 #endif /* LWIP_TCP */
 
-#endif /* LWIP_HDR_TCP_H */
+#endif /* LWIP_HDR_TCP_PRIV_H */