Sync io_uring.h header with 5.6 kernel bits
Sync io_uring.h header with 5.6 kernel bits

Just IOSQE_ASYNC was missing.

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing