selftests/bpf: Adding a namespace reset for tc_redirect

This patch delete ns_src/ns_dst/ns_redir namespaces before recreating
them, making the test more robust.

Signed-off-by: Yucong Sun <sunyucong@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211025223345.2136168-5-fallentree@fb.com