Enable direct IO for passthrough examples when open has flag O_DIRECT

Enable direct IO for passthrough examples when open has flag O_DIRECT

Shared locks (parallel_direct_writes) cannot be enabled for O_DIRECT, as
O_DIRECT may be set past file open time with fcntl(fd, F_SETFD, ...).
Kernel side fuse has precautions for shared lock direct-IO (direct_io in
libfuse), as it needs an exclusive inode lock when direct and page cache
IO happend at the same time.

In order to enjoy the parallel_direct_writes feature (i.e., get a shared
lock, not exclusive lock) for writes to the same file), direct_io is needed.
The feature direct_io is corresponding to FOPEN_DIRECT_IO in fuse kernel.
FOPEN_DIRECT_IO and O_DIRECT are not entirely the same as described above.
So enable direct_io (i.e., FOPEN_DIRECT_IO in fuse kernel) to enjoy parallel
direct_writes.

Some patches related to FOPEN_DIRECT_IO and O_DIRECT are below:

https://lore.kernel.org/all/753d6823-e984-4730-a126-d66b65ea772c@ddn.com