io_uring: add fgetxattr and getxattr support

This adds support to io_uring for the fgetxattr and getxattr API.

Signed-off-by: Stefan Roesch <shr@fb.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20220323154420.3301504-5-shr@fb.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>