selftests/bpf: add a test for overlapping packet range checks

add simple C test case for llvm and verifier range check fix from
commit b1977682 ("bpf: improve verifier packet range checks")

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>