gbinder_writer_append_fd() duplicates the descriptor and appends
the duplicate to the parcel. The caller may immediately close its
descriptor.
gbinder_reader_read_fd() fetches the descriptor from the parcel
without duplicating it. The descrriptor will be closed as soon as
the library has finished processing the request. Returns -1 on error.
gbinder_reader_read_dup_fd() fetches descriptor from the parcel
and dups it. The caller is responsible for closing the returned
descriptor. Returns -1 on failure.
