Some new verifier tests that hit some important gaps in the parameter
space for atomic ops.

There are already exhaustive tests for the JIT part in
lib/test_bpf.c, but these exercise the verifier too.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211015093318.1273686-1-jackmanb@google.com