ceph: pass an idmapping to mknod/symlink/mkdir

Enable mknod/symlink/mkdir iops to handle idmapped mounts.
This is just a matter of passing down the mount's idmapping.

Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>