isisd: consider link local ipv4 addresses as valid

isisd: consider link local ipv4 addresses as valid

It is not possible to create an adjacency by using interface
addresses within the `169.254.0.0/24` pool.

When forging the IIH messages, the interface addresses from
that pool are not appended:

> Neither IPv4 nor IPv6 considered usable. Ignoring IIH

Using this network pool is possible on other IS-IS
implementations. Let us authorize to use such network
addresses.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>