fuse: add stubbed-out unimplemented functions
fuse: add stubbed-out unimplemented functions

The struct fuse_operations has more member functions than we've
implemented.  List the unimplemented ones guarded with an `#if 0`.

Signed-off-by: Ramkumar Ramachandra <5c355d1d38066ed0c5de420d67c1b5ed0687c4bd@gmail.com>

artagnon/phoenixfs,artagnon/phoenixfs,artagnon/phoenixfs