vxlan: Allow setting destination to unicast address.

This patch allows setting VXLAN destination to unicast address.
It allows that VXLAN can be used as peer-to-peer tunnel without
multicast.

v4: generalize struct vxlan_dev, "gaddr" is replaced with vxlan_rdst.
    "GROUP" attribute is replaced with "REMOTE".
    they are based by David Stevens's comments.

v3: move a new attribute REMOTE into the last of an enum list
    based by Stephen Hemminger's comments.

v2: use a new attribute REMOTE instead of GROUP based by
    Cong Wang's comments.

Signed-off-by: Atzm Watanabe <atzm@stratosphere.co.jp>
Acked-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 6b35c42..9922704 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -296,7 +296,7 @@
 enum {
 	IFLA_VXLAN_UNSPEC,
 	IFLA_VXLAN_ID,
-	IFLA_VXLAN_GROUP,
+	IFLA_VXLAN_REMOTE,
 	IFLA_VXLAN_LINK,
 	IFLA_VXLAN_LOCAL,
 	IFLA_VXLAN_TTL,