netd: let Fuzix choose local port

[beretta42]

as per issue #555
"uIP needs tweaking so that it uses the bind() provided local socket if presetn when we connect()."

if we pass a local port of 0 to uip, it'll choose the local port, else it'll use fuzix's idea of the port no. is there a reason even to bother with uip picking it's local port?

[EtchedPixels]

There should no case where 0 ever gets passed.