Revert "SEBA-357 remove OLTDevice.uplink_port"

This reverts commit b32c5841731b844597465fb92810c82e86337021.

Change-Id: Ie17a784e703e3a204829bb7a208e6924d20e520f
diff --git a/xos/synchronizer/models/volt.xproto b/xos/synchronizer/models/volt.xproto
index cc9b652..60fb08d 100644
--- a/xos/synchronizer/models/volt.xproto
+++ b/xos/synchronizer/models/volt.xproto
@@ -34,6 +34,7 @@
     optional string of_id = 13 [help_text = "openflow id", db_index = False, feedback_state = True];
     optional string dp_id = 14 [help_text = "datapath id", db_index = False];
 
+    required string uplink = 15 [help_text = "uplink port", db_index = False];
     required string driver = 16 [default="voltha", help_text = "Olt driver", db_index = False];
 
     optional string switch_datapath_id = 17 [help_text = "Fabric switch to which the OLT is connected", db_index = False];