The current code ignores the address as passed to the BSD socket
function bind().  It seems that that may not have been possible with
earlier versions of the net API?  I discovered by reading the code and
experimentation that this seems to work fine in the current net API, so
this implements it for BSD sockets.

I removed some previous code that did not make sense to me, so you may
want to check that I did not screw up.  What I mean is "bind *" in
bind() and about "bind 0" in listen().

The handling when ports < 0 are specified is not consistent yet.  Either
we should normalize the ports to be at least 0, or we should return an
error condition for ports < 0.

The documentation in the man page ip(3) for the control commands "bind"
and "announce" does not mention the local address, should that be fixed,
too?