Fix incorrect function declaration

include/hexagram/pcapng.h

@@ -2,6 +2,7 @@
 #define _HEXAGRAM_PCAPNG_H
 
 #include <stdint.h>
+#include <sys/types.h>
 
 enum {
     HEXAGRAM_PCAPNG_ERROR_OK        = 0,
@@ -22,7 +23,7 @@ typedef struct _hexagram_pcapng_footer {
 
 typedef int (hexagram_pcapng_block_handler)(int fd,
                                             uint32_t type,
-                                            uint32_t length);
+                                            size_t length);
 
 ssize_t hexagram_pcapng_stream_read(int fd,
                                     hexagram_pcapng_block_handler *handler,