jail: Fix regression panic from eb8dcdeac22d

jail: Fix regression panic from eb8dcdeac22d

And possibly infinite loop calling prison_ip_restrict() in
kern_jail_set() [2].

[1] It is possible that prisons do not have any IPv4 or IPv6 addresses.
[2] If prison_ip_restrict() is not provided with prison_ip, when it
    allocates prison_ip successfully, then it should return false to
    indicate not redo prison_ip_restrict() later.

Reviewed by:	glebius
Approved by:	kp (mentor)
Fixes:	eb8dcdeac22d jail: network epoch protection for IP address lists
Differential Revision:	https://reviews.freebsd.org/D37906