Add missing include of stdio.h.

MFC after:	3 days
Sponsored by:	Juniper Networks, Inc.

tools/regression/netinet/tcpfullwindowrst/tcpfullwindowrsttest.c

@@ -35,6 +35,7 @@ $FreeBSD$
 #include <poll.h>
 #include <unistd.h>
 #include <signal.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>