Since BPF's bpf_user_rnd_u32() was introduced, there have been three
significant developments in the RNG: 1) get_random_u32() returns the
same types of bytes as /dev/urandom, eliminating the distinction between
"kernel random bytes" and "userspace random bytes", 2) get_random_u32()
operates mostly locklessly over percpu state, 3) get_random_u32() has
become quite fast.
So rather than using the old clunky Tausworthe prandom code, just call
get_random_u32(), which should fit BPF uses perfectly.