/*
 * Set the length of an audio stream (in seconds).
 *
 * Note: This method is optional, but if it is called, it must be called
 * after MusicBrainz::TRM#pcm_data and before any calls to
 * MusicBrainz::TRM#generate_signature.
 *
 * Aliases:
 *   MusicBrainz::TRM#set_length
 *   MusicBrainz::TRM#song_length=
 *   MusicBrainz::TRM#set_song_length
 *
 * Examples:
 *   trm.length = 4000
 */
static VALUE mb_trm_set_length(VALUE self, VALUE len) {