And possible infinite loop calling `prison_ip_restrict()` in `kern_jail_set()` [2].
[1] It is possible that prisons have no IPv4 or IPv6 addresses.
[2] If `prison_ip_restrict()` is not provided prison_ip, when it allocates prison_ip successfully, it should return false, to indicate not redo `prison_ip_restrict()`.
Fixes: eb8dcdeac22d jail: network epoch protection for IP address lists