face: increase tolerance in WebSocketChannel test

Face/TestWebSocketChannel/SetPingInterval now allows 80ms
absolute tolerance, so that the test case is more stable on
slower machines.

refs #4244

Change-Id: I897f3b33a0ea2eb9006f0dd8d70ef2a4624953e2
diff --git a/tests/daemon/face/websocket-channel.t.cpp b/tests/daemon/face/websocket-channel.t.cpp
index 8c45af8..a714291 100644
--- a/tests/daemon/face/websocket-channel.t.cpp
+++ b/tests/daemon/face/websocket-channel.t.cpp
@@ -287,13 +287,13 @@
 
 BOOST_AUTO_TEST_CASE(SetPingInterval)
 {
-  auto pingInterval = time::milliseconds(300);
+  const time::milliseconds pingInterval(800);
   auto address = getTestIp<AddressFamily::V4>(LoopbackAddress::Yes);
   SKIP_IF_IP_UNAVAILABLE(address);
   this->initialize(address, pingInterval, time::milliseconds(1000));
 
   BOOST_CHECK_EQUAL(limitedIo.run(2, // clientHandlePing
-                    time::seconds(1)), LimitedIo::EXCEED_OPS);
+                    pingInterval * 3), LimitedIo::EXCEED_OPS);
   BOOST_CHECK_LE(measuredPingInterval, pingInterval * 1.1);
   BOOST_CHECK_GE(measuredPingInterval, pingInterval * 0.9);
 }