include/netinet/if_ether.h: add ethhdr definition.

adapts to third-party code compilation. in the process of porting EtherCAT,
we encounter some situations where the structure is not defined, or the
returned data types do not match the expectations. Refer to the EtherCAT
implementation of other systems and add relevant definitions.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

Author: zhhyu7

include/netinet/if_ether.h

@@ -40,6 +40,17 @@
 #define ETH_P_IP  ETHERTYPE_IP
 #define ETH_P_ARP ETHERTYPE_ARP
 
+/****************************************************************************
+ * Public Type Definitions
+ ****************************************************************************/
+
+struct ethhdr
+{
+  uint8_t  h_dest[ETH_ALEN];      /* destination eth addr    */
+  uint8_t  h_source[ETH_ALEN];    /* source ether addr    */
+  uint16_t h_proto;               /* packet type ID field    */
+};
+
 /* Ethernet Address Resolution Protocol.
  *
  * See RFC 826 for protocol description.  Structure below is adapted