(socket server) do not create a select interrupt object everytime when polling for notifications while waiting for new connections, instead use a persistent one which is a member variable

ixwebsocket/IXSelectInterrupt.cpp

@@ -8,6 +8,9 @@
 
 namespace ix
 {
+    const uint64_t SelectInterrupt::kSendRequest = 1;
+    const uint64_t SelectInterrupt::kCloseRequest = 2;
+
     SelectInterrupt::SelectInterrupt()
     {
         ;