add one more bogus legacy header

this one is for program(s|ers) who haven't heard of uint16_t and
uint32_t (which are obviously the correct types for use in such
situations, as they're the argument/return types for ntohs/htons and
ntohl/htonl).

include/netinet/in_systm.h

+#ifndef _NETINET_IN_SYSTM_H
+#define _NETINET_IN_SYSTM_H
+
+#include <stdint.h>
+
+typedef uint16_t n_short;
+typedef uint32_t n_long, n_time;
+
+#endif