InnoDB RNG maintains global state, causing otherwise unnecessary bus
traffic. Even worse, this is cross-mutex traffic. That is, different
mutexes suffer from contention.

Fixed delay of 4 was verified to give best throughput by OLTP update
index and read-write benchmarks on Intel Broadwell (2/20/40) and
ARM (1/46/46).

This is a backport of ce047900 from
MariaDB Server 10.3.