pidl/ws: fix -Wmissing-prototype

pidl/ws: fix -Wmissing-prototype

Port Wireshark commit e759d82

Author: Alexis La Goutte <alexis.lagoutte@gmail.com>
Date:   Fri Sep 26 18:47:53 2014 +0200

    PIDL: fix -Wmissing-prototype

    Change-Id: I4cae47450e8026b10bd373828f235184560e0a99
    Reviewed-on: https://code.wireshark.org/review/4308
    Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
    Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
    Reviewed-by: Michael Mann <mmann78@netscape.net>
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>