ceph: fix setting of xattrs on async created inodes

Currently when we create a file, we spin up an xattr buffer to send
along with the create request. If we end up doing an async create
however, then we currently pass down a zero-length xattr buffer.

Fix the code to send down the xattr buffer in req->r_pagelist. If the
xattrs span more than a page, however give up and don't try to do an
async create.

Cc: stable@vger.kernel.org
URL: https://bugzilla.redhat.com/show_bug.cgi?id=2063929
Fixes: 9a8d03ca

 ("ceph: attempt to do async create when possible")
Reported-by: John Fortin <fortinj66@gmail.com>
Reported-by: Sri Ramanujam <sri@ramanujam.io>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>