ioc: shutdown PVA server via epicsAtExit()

Otherwise is shutdown in global dtor.
Better to use epicsAtExit() which has
some ordering

src/ioc/PVAServerRegister.cpp

@@ -103,10 +103,16 @@ void pvasr(int lvl)
     }
 }
 
+void pva_server_cleanup(void *)
+{
+    stopPVAServer();
+}
+
 void initStartPVAServer(initHookState state)
 {
     pvd::Lock G(the_server_lock);
     if(state==initHookAfterIocRunning && !the_server) {
+        epicsAtExit(&pva_server_cleanup, 0);
         startitup();
 
     } else if(state==initHookAtIocPause) {
@@ -114,7 +120,6 @@ void initStartPVAServer(initHookState state)
     }
 }
 
-
 void registerStartPVAServer(void)
 {
     epics::iocshRegister<const char*, &startPVAServer>("startPVAServer", "provider names");