Improve compiliation on NetBSD.

gtests/net/packetdrill/checksum.c

@@ -25,6 +25,7 @@
 #include "checksum.h"
 
 #include <assert.h>
+#include <stdint.h>
 
 /* Add bytes in buffer to a running checksum. Returns the new
  * intermediate checksum. Use ip_checksum_fold() to convert the

gtests/net/packetdrill/run_system_call.c

@@ -32,6 +32,7 @@
 #include <netinet/in.h>
 #include <poll.h>
 #include <pthread.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>