add ARPHDR_VSOCKMON from linux v4.12

new in linux commit 531b374834c891ae2abf800693074df35a7d1a36

include/net/if_arp.h

@@ -92,6 +92,7 @@ struct arphdr {
 #define ARPHRD_IP6GRE 823
 #define ARPHRD_NETLINK 824
 #define ARPHRD_6LOWPAN 825
+#define ARPHRD_VSOCKMON 826
 
 #define ARPHRD_VOID	  0xFFFF
 #define ARPHRD_NONE	  0xFFFE