tool_metalink.c: Filtered resource URLs by type

In Metalink v3, the type attribute of url element indicates the
type of the resource the URL points to. It can include URL to the
meta data, such as BitTorrent metainfo file.  In Curl, we are not
interested in these meta data URLs. Instead, we are only
interested in the HTTP and FTP URLs. This change filters out
non-HTTP and FTP URLs. If we don't filter out them, it will be
downloaded by curl and hash check will fail if hash is provided
and next URL will be tried. This change will cut this useless
network transfer.