io_uring: expose read/write attribute capability

After commit 9a213d3b80c0, we can pass additional attributes along with
read/write. However, userspace doesn't know that. Add a new feature flag
IORING_FEAT_RW_ATTR, to notify the userspace that the kernel has this
ability.

Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
Reviewed-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Tested-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20241205062109.1788-1-anuj20.g@samsung.com


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