ipfw.8: Fix table example

Fix some erronous lines in the example section.

PR: 248943
Submitted by: Jose Luis Duran
Reviewers: ae, manpages (gbe)
Differential Revision: https://reviews.freebsd.org/D30191

(cherry picked from commit 802637be06457c7593692bdf79f8466fa5f54d4a)