schemas: legacy: enumerate 'ConnectsToType' field

Tested: Schema Validator Pass

Change-Id: I53f2d9e8ec0b07d572bc5c61484fe786e06d06c7
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index 15326b5..601c52c 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -721,7 +721,8 @@
                 "type": "object"
             },
             "ConnectsToType": {
-                "type": "string"
+                "type": "string",
+                "const": "MB Upstream Port"
             },
             "CpuID": {
                 "type": "number"