[extractor/common] Return MPD manifest as format's url meta field (#20242)

For symmetry with other segmented media

youtube_dl/extractor/common.py

@@ -2120,7 +2120,7 @@ class InfoExtractor(object):
                         bandwidth = int_or_none(representation_attrib.get('bandwidth'))
                         f = {
                             'format_id': '%s-%s' % (mpd_id, representation_id) if mpd_id else representation_id,
-                            'url': base_url,
+                            'url': mpd_url,
                             'manifest_url': mpd_url,
                             'ext': mimetype2ext(mime_type),
                             'width': int_or_none(representation_attrib.get('width')),