bpf: add couple of test cases for div/mod by zero

Add couple of missing test cases for eBPF div/mod by zero to the
new test_verifier prog runtime feature. Also one for an empty prog
and only exit.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>