(legacy) change behaviour of associated nat rules (https://github.com/opnsense/core/issues/695), show rule but hide edit and duplicate buttons

If for some reason a config has "typeless" rules, which don't belong to any active nat rule the user won't notice this anymore (and doesn't have the ability to remove them).
This can happen with imports from old configs for example or manually changed configs.

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Closes #726

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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
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PR: https://forum.opnsense.org/index.php?topic=2012.0
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(cherry picked from commit 31952088)

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

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(cherry picked from commit ffc5ef3a)

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

(cherry picked from commit fd395c71)

(cherry picked from commit 27b4d61b)

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

(cherry picked from commit 394ad989)

(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

(cherry picked from commit 1be61431)

(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

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