Minor DT config fix, 7 is the common c_tag on the ONU/ONTs, not using it for the OLT s_tag

Change-Id: I114f0156ab745c4cb004f6345cc7dad36927c8d7
diff --git a/tests/data/bbsim-kind-dt.yaml b/tests/data/bbsim-kind-dt.yaml
index 1955c45..6309371 100644
--- a/tests/data/bbsim-kind-dt.yaml
+++ b/tests/data/bbsim-kind-dt.yaml
@@ -38,7 +38,7 @@
     -
       onu: 'BBSM00000001'
       c_tag: '4096'
-      s_tag: '7'
+      s_tag: '900'
 
   dst:
     - ip: null