jail: Avoid multipurpose return value of function prison_ip_restrict()

[zlei]

Summary

Currently function prison_ip_restrict() returns true if the replacement buffer was used, or no buffer provided and allocation fails and should redo. The logic is confusion and cause possibly infinite loop from eb8dcdeac22d .

No functional change intended.

[jamie]

It took me longer to remember what I had done in the first place than it did to understand the new logic. I like this.

[kp]

Approved by: kp (mentor)

[glebius]

sys/kern/kern_jail.c

2048–2049

Type of redo_ip4 can be changed to bool and this expression reduced to:

redo_ip4 = !prison_ip_restrict(tpr, PR_INET, &ip4);

Same applies to redo_ip6.

[zlei]

I'm planning to do this on stable branches.

@glebius
Do you have any plans to MFC eb8dcdeac22d (and related fixes)?
If no I'd prefer commit this separately (from D37906) so it is easy to track and review.

[zlei]

sys/kern/kern_jail.c

2048–2049

Good catch!