List extended attribute names
If size is zero, the total size of the attribute list should be sent with fuse_reply_xattr.
If the size is non-zero, and the null character separated attribute list fits in the buffer, the list should be sent with fuse_reply_buf.
If the size is too small for the list, the ERANGE error should be sent.
Valid replies: fuse_reply_buf fuse_reply_xattr fuse_reply_err