Client: bump ll_ref from int32 to uint64_t

Client: bump ll_ref from int32 to uint64_t

ll_ref can surge up if application repeatly lookup same dentry
and finally cause overflow.

https://tracker.ceph.com/issues/40775 is an example.

in kernel fuse driver and libfuse, uint64_t is used, update
ceph-fuse side to match.

Fixes: https://tracker.ceph.com/issues/40775
Signed-off-by: Xiaoxi CHEN <xiaoxchen@ebay.com>
(cherry picked from commit bb46de885336a8cd2adc9c0507e543c6832346e7)

 Conflicts:
	src/client/Client.h
        use new code, skip all non-toched changes.
	src/client/Inode.h
        use new code.