libnl: Move the pthread dependency menu comment

In order for this comment to be properly displayed, it must be moved to be
at the end of the file.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>