selftests: mlxsw: Add tc sample tests for new triggers

Test that packets are sampled when tc-sample is used with matchall
egress binding and flower classifier. Verify that when performing
sampling on egress the end-to-end latency is reported as metadata.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>