selftests: traceroute: Add ICMP extensions tests

selftests: traceroute: Add ICMP extensions tests

Test that ICMP extensions are reported correctly when enabled and not
reported when disabled. Test both IPv4 and IPv6 and using different
packet sizes, to make sure trimming / padding works correctly.

Disable ICMP rate limiting (defaults to 1 per-second per-target) so that
the kernel will always generate ICMP errors when needed.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20251027082232.232571-4-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>