fuse: invalidate dentry on EEXIST creates or ENOENT deletes

The EEXIST errors returned from server are strong sign that a local
negative dentry should be invalidated.  Similarly, The ENOENT errors from
server can also be a sign of revalidate failure.

This commit invalidates dentries on EEXIST creates and ENOENT deletes by
calling fuse_invalidate_entry(), which improves the consistency with no
performance degradation.

Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>