selftests/bpf: Use vmlinux.h in test_xdp_meta

- Replace linux/* includes with vmlinux.h
- Include errno.h
- Include bpf_tracing_net.h for TC_ACT_* and ETH_*
- Use BPF_STDERR instead of BPF_STREAM_STDERR

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260218215651.2057673-2-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>