[MACVLAN]: Update Kconfig to refer to iproute

Since the macvlan release I had at least 5 users asking how to configure
it since the old userspace tool doesn't work with the version in the
kernel. Add a pointer to the Kconfig help.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -90,6 +90,11 @@ config MACVLAN
 	  This allows one to create virtual interfaces that map packets to
 	  or from specific MAC addresses to a particular interface.
 
+	  Macvlan devices can be added using the "ip" command from the
+	  iproute2 package starting with the iproute2-2.6.23 release:
+
+	  "ip link add link <real dev> [ address MAC ] [ NAME ] type macvlan"
+
 	  To compile this driver as a module, choose M here: the module
 	  will be called macvlan.