sch_cake: Fix tin order when set through skb->priority

In diffserv mode, CAKE stores tins in a different order internally than
the logical order exposed to userspace. The order remapping was missing
in the handling of 'tc filter' priority mappings through skb->priority,
resulting in bulk and best effort mappings being reversed relative to
how they are displayed.

Fix this by adding the missing mapping when reading skb->priority.

Fixes: 83f8fd69 ("sch_cake: Add DiffServ handling")
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>