Disable tests that will fail when rwengine=off

Disable tests that will fail when rwengine=off

When ENABLE_LLVM_NATIVECODEGEN is OFF, the bpf module rw_engine code
will not be used. This is the code that generates custom sscanf and
printf functions for BPF map defs. These generated functions are used
to serialize arguments to update_value (and similar calls which take
string as input) to the correct key / value types.

It's still possible to use update_value and its ilk without rw_engine
enabled, just need to use the variants that take raw bytes and do
serialization manually. In the future we can add some simple
sscanf/printfs for common types that can be used without LLVM
generation.

For now, when rw_engine is disabled, it's fine to skip tests that
require these autogenerated functions.