selftests/bpf: Fix a test_verifier failure

The following test_verifier subtest failed due to
new encoding for BSWAP.

  $ ./test_verifier
  ...
  #99/u invalid 64-bit BPF_END FAIL
  Unexpected success to load!
  verification time 215 usec
  stack depth 0
  processed 3 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
  #99/p invalid 64-bit BPF_END FAIL
  Unexpected success to load!
  verification time 198 usec
  stack depth 0
  processed 3 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0

Tighten the test so it still reports a failure.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011244.3717464-1-yonghong.song@linux.dev


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