selftests/tc-testing: Add test for echo of big TC filters

selftests/tc-testing: Add test for echo of big TC filters

Add a selftest that checks whether the kernel can successfully echo a
big tc filter, to test the fix introduced in commit:

369609fc6272 ("tc: Ensure we have enough buffer space when sending filter netlink notifications")

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20250410104322.214620-1-toke@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>