Hints: Add basic benchmark module for traits proposal

[netoptimizer]

This benchmark module depend on a kernel feature (currently) called "traits"

Tested on top of kernel tree and branch:

• https://github.com/arthurfabre/linux/tree/afabre/traits-002-bounds-inline

I had to export the following functions via EXPORT_SYMBOL_GPL() to make it compile:

• bpf_xdp_trait_set
• bpf_xdp_trait_get
• bpf_xdp_trait_del

Initial result show that overhead is too large to be acceptable for XDP.

• More optimizations for traits are needed

This bench kernel module can be used for guiding our optimizations.

Cc. @tohojo , @arthurfabre , @LorenzoBianconi