net: if_arp: add ARPHRD_NETLINK type

This small patch adds the definition of ARPHRD_NETLINK which can for
example be used by netlink monitoring devices as device type. So that
sockaddr_ll can pick it up and based on that choose the correct packet
dissector.
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/uapi/linux/if_arp.h

@@ -93,6 +93,7 @@
 #define ARPHRD_PHONET_PIPE 821		/* PhoNet pipe header		*/
 #define ARPHRD_CAIF	822		/* CAIF media type		*/
 #define ARPHRD_IP6GRE	823		/* GRE over IPv6		*/
+#define ARPHRD_NETLINK	824		/* Netlink header		*/
 
 #define ARPHRD_VOID	  0xFFFF	/* Void type, nothing is known */
 #define ARPHRD_NONE	  0xFFFE	/* zero header length */