Add support for --loginuid-immutable

[dmlary]

Please add support for the --loginuid-immutable flag that is available to auditctl. This prevents an administrative user from changing their audit uid once it has been set. It is implemented as a feature. This functionality could help wider adoption of auditbeat.

https://github.com/linux-audit/audit-userspace/blob/de35e6f18212e03e9ca57124ce5362c26aae22a2/lib/libaudit.c#L586-L595