vfs_ceph: add fake async pwrite/pread send/recv hooks

vfs_ceph: add fake async pwrite/pread send/recv hooks

As found by Jeremy, VFS modules that don't provide pread_send() or
pwrite_send() hooks result in vfs_default fallback, which is
catastrophic for VFS modules with non-mounted filesystems such as
vfs_ceph.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13425

Reported-by: Jeremy Allison <jra@samba.org>
Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
(cherry picked from commit f0e6453b0420fe9d062936d4ddc05f44b40cf2ba)