bpf, selftests: Update array map tests for per-cpu batched ops

Follows the same logic as the hashtable tests.

Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210424214510.806627-3-pctammela@mojatatu.com