client: when STATX_NLINK is requested request FsLs caps

client: when STATX_NLINK is requested request FsLs caps

We currently determine the getattr request mask prior to doing the
lookup, so we don't necessarily know whether the terminal entry is
a directory or something else.

Directory nlink count is governed by the dirstats, and those are
under Fs caps. Request both Fs and Ls if the request mask includes
STATX_NLINK.

Fixes: https://tracker.ceph.com/issues/48313
Signed-off-by: Jeff Layton <jlayton@redhat.com>
(cherry picked from commit e2ea2214cbb1ff4bd7332bb28db4f3477efb37df)