bpf: add test cases to bpf selftests to cover all access tests

Lets add test cases to cover really all possible direct packet
access tests for good/bad access cases so we keep tracking them.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>