ipf.5: revert C style(9) applied to man page

These changes were made by accident in:

ipfilter: Adjust userland returns to conform to style(9)
2582ae5740181e0d2bab10003d66ae91c9b56329

That commit made similar mistakes in other man pages, but those have
already been fixed.

Signed-off-by: Graham Percival <gperciva@tarsnap.com>
Reviewed by: mhorne
Sponsored by: Tarsnap Backup Inc.
Pull Request: https://github.com/freebsd/freebsd-src/pull/1433