pfSense

Add address family validation, also hide gateways or gateway groups from the gateway list.
Fix Ticket #1659

Add address family input validation on the Gateways edit page, also prevent adding gateways on interfaces that do not carry that address family.
Fix Ticket #1633

Automatically adjust the subnet size drop down when editing a entry
Ticket #1661

Add Address Family input validation on the system routes edit page. Do not allow IPv4 subnet masks > 32 bits.
Ticket #1661

Fix the address family check to skip empty DNS gateway fieldS

Change the DNS interface code to DNS gateway code. This will need upgrade code for existing configs.

Simplify this code a bit, should be the same test in both locations since this should be either/or, and with the other code it can apparently fall into a trap where it shows neither.

Fix field name label.

un-break services_dhcpv6.php

Clarify advertising options, add router only type.