net: add ARP hardware type defintions

These are required for DHCPv6 to identify the type of a link-layer
address (for DUID creation).

sys/include/net/arp.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2018 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @defgroup    net_arp    Address resolution protocol (ARP)
+ * @ingroup     net_ipv4
+ * @brief       ARP definitions
+ * @{
+ *
+ * @file
+ * @brief   ARP definitions
+ *
+ * @author  Martine Lenders <m.lenders@fu-berlin.de>
+ */
+#ifndef NET_ARP_H
+#define NET_ARP_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @name    Hardware types
+ * @anchor  net_arp_hwtype
+ * @see     [IANA ARP parameters]
+ *          (https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#table-arp-parameters-2)
+ * @{
+ */
+#define ARP_HWTYPE_ETHERNET (1U)        /**< Ethernet */
+#define ARP_HWTYPE_EUI64    (27U)       /**< EUI-64 */
+/** @} */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NET_ARP_H */
+/** @} */