Feature: configurable IPv6 Link-Local address

[djGrrr]

Link-Local addresses should be configurable for interfaces when using Static IPv6.

It can be very useful to be able to set link-local ips for a router, fe80::1 is commonly used for the "internal side" of a router so that no matter what range an IPv6 network might be using on various interfaces, you can always use a gateway address of fe80::1

For the implementation, if an interface does not yet have any IPv6 configured, ie, not inet6 addresses, it is as simple as:
ifconfig ixv0 inet6 fe80::1/64 -auto_linklocal

If IPv6 is already configured, you must first remove all inet6 addresses; first standard ipv6, followed by link-local, then you can run the above command to configure the static link-local.

On the UI side, there would simply need to be an additional optional field for setting the link-local ip when configuring Static IPv6 that only allows you to set the ip, not the bits, which should be /64. For validation, the ip only need's to be within fe80::/64

[AdSchellevis]

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