There are a few cases where the gateway code is eligible
to drop a gateway on grounds of being disabled, inactive,
unconfigured or where the actual interface assigned is
disabled.  This is undesire because users that configure
a gateway won't be able to use it.

There are no bad side effects from the former by selecting
a whatsoever dysfunctional gateway, because the problem still
has to be fixed by the user in the gateway setup itself.

Worst of all, removing a disabled but used gateway makes
it not show up on edit, effectively wiping its setting on
save.  This breaks POLA.

While there, also enable the null routes for IPv4 and IPv6.

PR: https://forum.opnsense.org/index.php?topic=2100

PR: https://forum.opnsense.org/index.php?topic=2012.0

Lookie how far we've come...

(legacy) unbound renders some illegal output for empty ipv6, closes https://github.com/opnsense/core/issues/738

(legacy) curly braces in unbound.inc, fix $numprocs in the process. closes https://github.com/opnsense/core/issues/736

(legacy) missing dependency, fixes PHP Fatal error:  Call to undefined function is_private_ip() in /usr/local/etc/inc/services.inc on line 1750

(legacy) suppress warning for socket_sendto(): Host lookup failed [-10004]: No address associated with name in /usr/local/etc/inc/notices.growl.class on line 79

(legacy) fix for PHP Warning:  in_array() expects parameter 2 to be array, null given in /usr/local/www/interfaces_bridge_edit.php on line 605