vfs_xattr_tdb: add "xattr_tdb:ignore_user_xattr" option

vfs_xattr_tdb: add "xattr_tdb:ignore_user_xattr" option

Allows passing on "user." xattr to the backend. This can be useful for testing
specific aspects of operation on streams when "streams_xattr" is configured as
stream filesystem backend.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15126
MR: https://gitlab.com/samba-team/samba/-/merge_requests/2643

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
(cherry picked from commit 92e0045d7ca7c0b94efd0244ba0e426cad0a05b6)