core: compile io_wait support even if -DUSE_TCP is not set

io_wait is needed now also by the ctl module, so it should be
compiled even if no tcp support is desired.
Its compilation can be turned off if NO_IO_WAIT is defined
(but in this case one must make sure so no other piece of code
using it will be compiled).

io_wait.c

@@ -29,7 +29,7 @@
 
 
 
-#ifdef USE_TCP /* for now it make sense only with tcp */
+#ifndef NO_IO_WAIT
 
 #ifdef HAVE_EPOLL
 #include <unistd.h> /* close() */
@@ -631,4 +631,4 @@ void destroy_io_wait(io_wait_h* h)
 
 
 
-#endif
+#endif /*ifndef NO_IO_WAIT */