[Vnet] Set BFD multihop to true for Vnet routes (sonic-net#2244)

* Set BFD multihop to true for Vnet routes

Author: prsunny

orchagent/vnetorch.cpp

@@ -1539,6 +1539,8 @@ void VNetRouteOrch::createBfdSession(const string& vnet, const NextHopKey& endpo
         FieldValueTuple fvTuple("local_addr", src_ip.to_string());
         data.push_back(fvTuple);
 
+	data.emplace_back("multihop", "true");
+
         bfd_session_producer_.set(key, data);
 
         bfd_sessions_[monitor_addr].bfd_state = SAI_BFD_SESSION_STATE_DOWN;

tests/test_vnet.py

@@ -450,7 +450,7 @@ def get_bfd_session_id(dvs, addr):
         status, fvs = tbl.get(entry)
         fvs = dict(fvs)
         assert status, "Got an error when get a key"
-        if fvs["SAI_BFD_SESSION_ATTR_DST_IP_ADDRESS"] == addr:
+        if fvs["SAI_BFD_SESSION_ATTR_DST_IP_ADDRESS"] == addr and fvs["SAI_BFD_SESSION_ATTR_MULTIHOP"] == "true":
             return entry
 
     return None