[VOL-936] Add changes in voltctl for Onu distance from OLT

Change-Id: If3d7a3f72ac876f495f202f928d244b1ee6e64c5
diff --git a/internal/pkg/commands/funcmap.go b/internal/pkg/commands/funcmap.go
index 12d470f..6de9810 100644
--- a/internal/pkg/commands/funcmap.go
+++ b/internal/pkg/commands/funcmap.go
@@ -149,6 +149,9 @@
 	"device-port-disable": {
 		"v3": "voltha.VolthaService/DisablePort",
 	},
+	"get-ext-value": {
+		"v3": "voltha.VolthaService/GetExtValue",
+	},
 }
 
 // Get the descriptor source using the current ApiVersion setting