Also include <netinet/in.h> needed for IPPROTO_TCP.

Fixes build on NetBSD.

diff --git a/sacc.c b/sacc.c
index 86c522c..ec4742c 100644
--- a/sacc.c
+++ b/sacc.c
@@ -1,6 +1,7 @@
 /* See LICENSE file for copyright and license details. */
 #include <errno.h>
 #include <fcntl.h>
+#include <netinet/in.h>
 #include <netdb.h>
 #include <stdarg.h>
 #include <stdio.h>