[PKT_SCHED]: GRED: Remove auto-creation of default VQ

Since we are no longer depending on the default VQ to be always
allocated we can leave it up to the user to actually create it.
This gives the user the ability to leave it out on purpose and
enqueue packets directly to the device without applying the RED
algorithm.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>