Correct several typos, etc. in jail chapter:

• Correct misuse of '.' and '_'
• ntohl() converts from network order to host order, which is described oppositely.
• Userland jail.c does not do fork() before execve(), reflect the fact.
• prison_ip() returns 0 when IP is owned by the current jail, and the arch handbook describes the opposite.

Submitted by: MQ <nodummy yeah net>
PR: docs/108676