add headers to make it compile under OpenBSD

- 'struct in6_addr' is defined in <netinet/in.h>
- 'AF_INET6' is defined in <sys/socket.h>

LICENSE

@@ -6,6 +6,7 @@ Copyright 2004 Ted Unangst <tedu@openbsd.org>
 Copyright 2004 Todd C. Miller <Todd.Miller@courtesan.com>
 Copyright 2017 Hiltjo Posthuma <hiltjo@codemadness.org>
 Copyright 2017 Quentin Rameau <quinq@fifth.space>
+Copyright 2018 Josuah Demangeon <mail@josuah.net>
 
 Permission to use, copy, modify, and/or distribute this software for any
 purpose with or without fee is hereby granted, provided that the above

http.c

@@ -3,11 +3,13 @@
 #include <ctype.h>
 #include <errno.h>
 #include <limits.h>
+#include <netinet/in.h>
 #include <regex.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>