bpf, tests: Add more ALU32 tests for BPF_LSH/RSH/ARSH

This patch adds more tests of ALU32 shift operations BPF_LSH and BPF_RSH,
including the special case of a zero immediate. Also add corresponding
BPF_ARSH tests which were missing for ALU32.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210809091829.810076-6-johan.almbladh@anyfinetworks.com