samples/bpf: xdp_redirect_cpu adjustment to reproduce teardown race easier
The teardown race in cpumap is really hard to reproduce. These changes
makes it easier to reproduce, for QA.
The --stress-mode now have a case of a very small queue size of 8, that helps
to trigger teardown flush to encounter a full queue, which results in calling
xdp_return_frame API, in a non-NAPI protect context.
Also increase MAX_CPUS, as my QA department have larger machines than me.