if: restore token ring ARP type to header

Recent removal of Token Ring breaks the build of iproute2.

Even though Token Ring support is gone from the kernel, it is worth
keeping the the definition of the TR ARP type to avoid breaking
userspace programs that use this file.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/if_arp.h

@@ -82,7 +82,7 @@
 #define ARPHRD_FCPL	786		/* Fibrechannel public loop	*/
 #define ARPHRD_FCFABRIC	787		/* Fibrechannel fabric		*/
 	/* 787->799 reserved for fibrechannel media types */
-/* 800 used to be used for token ring */
+#define ARPHRD_IEEE802_TR 800		/* Magic type ident for TR	*/
 #define ARPHRD_IEEE80211 801		/* IEEE 802.11			*/
 #define ARPHRD_IEEE80211_PRISM 802	/* IEEE 802.11 + Prism2 header  */
 #define ARPHRD_IEEE80211_RADIOTAP 803	/* IEEE 802.11 + radiotap header */