pfSense

Change route collection and output. Fixes #12257

All changes are on src/usr/local/www/diag_routes.php

• Change problematic use of sed for an equivalent and safer use of tail
  (to remove headers) and grep (to filter output).
• Restrict AJAX request to POST only
• Increase update period from 5 to 15 seconds
• Hardcode output headers, use gettext() and fix some column names
  and formatting
• Fix route table sorting
• If the GET request has a value for "filter", pre-fill that in the form