selftests/bpf: Update EFAULT {g,s}etsockopt selftests

Instead of assuming EFAULT, let's assume the BPF program's
output is ignored.

Remove "getsockopt: deny arbitrary ctx->retval" because it
was actually testing optlen. We have separate set of tests
for retval.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230511170456.1759459-3-sdf@google.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>