aio: add make_fdync_iocb()
aio: add make_fdync_iocb()

It is quite simple since fdsync doesn't accept any parameters other than the
file descriptor.

scylladb/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar,dreamsxin/seastar,cloudius-systems/seastar,cloudius-systems/seastar,dreamsxin/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar,dreamsxin/seastar,avikivity/seastar