pf: atomically increment state ids

[kp]

Summary

Rather than using a per-cpu state counter, and adding in the CPU id we
can atomically increment the number.
This has the advantage of removing the assumption that the CPU ID fits
in 8 bits.

Event: Aberdeen Hackathon 2022

[mjg]

This should use alloc_unr64 instead.

[kp]

Use alloc_unr64()