selftests/bpf: Make sure bpf_{g,s}et_retval is exposed everywhere

For each hook, have a simple bpf_set_retval(bpf_get_retval) program
and make sure it loads for the hooks we want. The exceptions are
the hooks which don't propagate the error to the callers:

- sockops
- recvmsg
- getpeername
- getsockname
- cg_skb ingress and egress

Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20220823222555.523590-6-sdf@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>