net/sched: cbs: Set default link speed to 10 Mbps in cbs_set_port_rate

The discussion to be made is absolutely the same as in the case of
previous patch ("taprio: Set default link speed to 10 Mbps in
taprio_set_picos_per_byte"). Nothing is lost when setting a default.

Cc: Leandro Dorileo <leandro.maciel.dorileo@intel.com>
Fixes: e0a7683d ("net/sched: cbs: fix port_rate miscalculation")
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>