audit_log_rotations is meant to not be dynamic, but can be changed with set global

Tested against PS 5.7.23-23.

audit_log_rotations is meant to be non-dynamic, however, it is possible to change its value with set global.

mysql [localhost] {root} ((none)) > set global audit_log_rotations=100;
Query OK, 0 rows affected (0.00 sec)

Note, it doesn't change anything (old value is used).

Steps to reproduce:

1. Configure MySQL with the below:

plugin-load=audit_log.so
audit_log_policy=ALL
audit_log_format=OLD
audit_log_file=/auditlog/audit.log
audit_log_rotate_on_size=512K 

 2. Change the value of audit_log_rotations with set global.