LU-14093 lnet: annotate LNET_WIRE_HANDLE_COOKIE_NONE as u64

LU-14093 lnet: annotate LNET_WIRE_HANDLE_COOKIE_NONE as u64

Fix the following warning on new gcc with -Wextra when including
lustre_idl.h on external project:

.../include/linux/lnet/lnet-types.h: In function LNetMDHandleIsInvalid:
.../include/linux/lnet/lnet-types.h:355:46:
   error: comparison of integer expressions of different signedness:
   int and __u64 {aka long long unsigned int} [-Werror=sign-compare]
        return (LNET_WIRE_HANDLE_COOKIE_NONE == h.cookie);
                                             ^~

Lustre-change: https://review.whamcloud.com/43713
Lustre-commit: 27214876fcdfbda016c920bce4ab1da800fcda4b

Change-Id: I05f21dcca5fe9dd15d1e0b6cb9a29c3999bcd807
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46215
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>