NET_NEEDS_GIANT removal

[Warner Losh]

> > i4b		- ISDN implementation
> ...
> 
> Before deleting we should replace i4b with the one from hps.
> http://www.selasky.org/hans_petter/isdn4bsd/index.html
> It was said to be GIANT free last time I asked.

Who has reviewed this code?  Last time I checked, it had all kinds of
Byzantine construts that made it extremely difficult to penetrate.
There were very few comments and it implemented state machines as
computed gotos :-(.  The cure would be worse than the disease.

Warner