sculpt: NIC ready only with IP other than 0.0.0.0

This patch refines the criterion of when the networking is considered as
ready to use. Until now, any IP reported by the NIC router was taken as
an indicator for connectivity. But as the NIC router reports an IP
0.0.0.0/32 when no network cable is plugged at the uplink, the condition
was too loose.

repos/gems/src/app/sculpt_manager/model/nic_state.h

@@ -35,7 +35,7 @@ struct Sculpt::Nic_state
 		return Nic_state { result };
 	}
 
-	bool ready() const { return ipv4.valid(); }
+	bool ready() const { return ipv4.valid() && ipv4 != "0.0.0.0/32"; }
 };
 
 #endif /* _MODEL__NIC_STATE_H_ */