selftests: concurrency: add test to verify parallel replace/delete

Implement test that runs 5 instances of tc replace filter in parallel with
5 instances of tc del filter from same tp instance. Each instance uses its
own filter handle and key range.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>