Add warning about upcoming removal of old Ethernet API

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/net/eth.c b/net/eth.c
index 3d93966..8e1d692 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -500,6 +500,8 @@
 }
 #elif defined(CONFIG_CMD_NET) && !defined(CONFIG_NET_MULTI)
 
+#warning Ethernet driver is deprecated.  Please update to use CONFIG_NET_MULTI
+
 extern int at91rm9200_miiphy_initialize(bd_t *bis);
 extern int mcf52x2_miiphy_initialize(bd_t *bis);
 extern int ns7520_miiphy_initialize(bd_t *bis);