selftests/bpf: validate replace of TC filters is working

Daniel discovered recently I broke TC filter replace (and fixed
it in commit ad9294db

 ("bpf: fix cls_bpf on filter replace")).
Add a test to make sure it never happens again.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>