selftests/bpf: test_xdp_veth: Remove unused defines

IP_CMD_MAX_LEN and NS_SUFFIX_LEN aren't used anywhere.

Remove these unused defines

Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@bootlin.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250131-redirect-multi-v4-2-970b33678512@bootlin.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>