libctrl: Include config.h so we can include netinet/tcp.h

In e15ac060e7ae78d4c3569d7fc9071bcf49807e05 we tried to fix
the nuttx build but we never included "netinet/tcp.h" after
it and the compiler warned about the unused "on" parameter
which we didn't notice because of the other warnings...

Include config.h so we can see if there is a tcp.h and then
include it.
diff --git a/src/ctrl/control_if.c b/src/ctrl/control_if.c
index dc19120..18e695d 100644
--- a/src/ctrl/control_if.c
+++ b/src/ctrl/control_if.c
@@ -21,6 +21,8 @@
  *
  */
 
+#include "config.h"
+
 #include <errno.h>
 #include <inttypes.h>
 #include <stdio.h>