selftests/bpf: skip verifier tests for unsupported map types

Use recently introduced bpf_probe_map_type() to skip tests in the
test_verifier if map creation (create_map) fails. It's handled
explicitly for each fixup, i.e. if bpf_create_map returns negative fd,
we probe the kernel for the appropriate map support and skip the
test is map type is not supported.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>