Sanity validate ntp response

timesource/timesource.go

@@ -73,6 +73,9 @@ func computeOffset(timeQuery ntpQuery, servers []string, allowedFailures int) (t
 			response, err := timeQuery(server, ntp.QueryOptions{
 				Timeout: DefaultRPCTimeout,
 			})
+			if err == nil {
+				err = response.Validate()
+			}
 			if err != nil {
 				responses <- queryResponse{Error: err}
 				return

timesource/timesource_test.go

@@ -39,7 +39,10 @@ func (tc *testCase) query(string, ntp.QueryOptions) (*ntp.Response, error) {
 		tc.actualAttempts++
 		tc.mu.Unlock()
 	}()
-	response := &ntp.Response{ClockOffset: tc.responses[tc.actualAttempts].Offset}
+	response := &ntp.Response{
+		ClockOffset: tc.responses[tc.actualAttempts].Offset,
+		Stratum:     1,
+	}
 	return response, tc.responses[tc.actualAttempts].Error
 }