selftests: mlxsw: qos_defprio: Convert from lldptool to dcb

Set up default port priority through the iproute2 dcb tool, which is easier
to understand and manage.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: mlxsw: qos_defprio: Use until_counter_is

Instead of hand-coding the busywait() predicate, use the until_counter_is()
introduced recently.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Amit Cohen <amitc@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: mlxsw: Add a self-test for port-default priority

Send non-IP traffic to a port and observe that it gets prioritized
according to the lldptool app=$prio,1,0 rules.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>