[bitmap_vnet]: Fix removal flow for tunnel route (sonic-net#1139)

There was a mistake in BITMAP VNET code that caused used_count for endpoints not to be decremented during removing tunnel route. As a result some SDK resources were not fully removed in case one endpoint is shared between two or more tunnel routes.

Signed-off-by: Volodymyr Samotiy <[email protected]>

orchagent/vnetorch.cpp

@@ -1102,7 +1102,7 @@ bool VNetBitmapObject::removeTunnelRoute(IpPrefix& ipPrefix)
         throw std::runtime_error("VNET tunnel route removal failed");
     }
 
-    auto endpointInfo = endpointMap_.at(endpoint);
+    auto& endpointInfo = endpointMap_.at(endpoint);
 
     sai_status_t status;