selftests/bpf: add testcase to verifier_bounds.c for BPF_JNE

Add testcase for the logic that the verifier tracks the BPF_JNE for regs.
The assembly function "reg_not_equal_const()" and "reg_equal_const" that
we add is exactly converted from the following case:

  u32 a = bpf_get_prandom_u32();
  u64 b = 0;

  a %= 8;
  /* the "a > 0" here will be optimized to "a != 0" */
  if (a > 0) {
    /* now the range of a should be [1, 7] */
    bpf_skb_store_bytes(skb, 0, &b, a, 0);
  }

Signed-off-by: Menglong Dong <menglong8.dong@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231219134800.1550388-5-menglong8.dong@gmail.com


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