posix: ensure in_addr_t and in_port_t defined via arpa/inet.h
The spec requires that `in_addr_t` and `in_port_t` are both
defined when `<arpa/inet.h>` is included.
They were added to `<netinet/in.h>` in the previous commit.
#ifndef ZEPHYR_INCLUDE_POSIX_ARPA_INET_H_
#define ZEPHYR_INCLUDE_POSIX_ARPA_INET_H_
+#include <stddef.h>
+
+#include <zephyr/posix/netinet/in.h>
+#include <zephyr/posix/sys/socket.h>
+
#include <zephyr/net/socket.h>
#ifdef __cplusplus
