selftests/bpf: Remove bpf_tracing_net.h usages from two networking tests

This patch removes the bpf_tracing_net.h usage from the networking tests,
fib_lookup and test_lwt_redirect. Instead of using the (copied) macro
TC_ACT_SHOT and ETH_HLEN from bpf_tracing_net.h, they can directly
use the ones defined in the network header files under linux/.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240509175026.3423614-2-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Add bpf_fib_lookup test

This patch tests the bpf_fib_lookup helper when looking up
a neigh in NUD_FAILED and NUD_STALE state. It also adds test
for the new BPF_FIB_LOOKUP_SKIP_NEIGH flag.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230217205515.3583372-2-martin.lau@linux.dev