mcast: define and use MRT[6]_MAX in ip[6]_mroute_opt()

This will ease further addition of new MRT[6]_* values and avoid to update
in6.h each time.
Note that we reduce the maximum value from 210 to 209, but 210 does not match
any known value in ip[6]_mroute_setsockopt().

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/in6.h b/include/uapi/linux/in6.h
index 5673b97..53b1d56 100644
--- a/include/uapi/linux/in6.h
+++ b/include/uapi/linux/in6.h
@@ -259,17 +259,10 @@
 
 /*
  * Multicast Routing:
- * see include/linux/mroute6.h.
+ * see include/uapi/linux/mroute6.h.
  *
- * MRT6_INIT			200
- * MRT6_DONE			201
- * MRT6_ADD_MIF			202
- * MRT6_DEL_MIF			203
- * MRT6_ADD_MFC			204
- * MRT6_DEL_MFC			205
- * MRT6_VERSION			206
- * MRT6_ASSERT			207
- * MRT6_PIM			208
- * (reserved)			209
+ * MRT6_BASE			200
+ * ...
+ * MRT6_MAX
  */
 #endif /* _UAPI_LINUX_IN6_H */