nic_router: != operator for IP address prefix

Ref #2670

repos/os/src/server/nic_router/ipv4_address_prefix.h

@@ -39,6 +39,12 @@ struct Net::Ipv4_address_prefix
 	Ipv4_address subnet_mask() const;
 
 	Ipv4_address broadcast_address() const;
+
+	bool operator != (Ipv4_address_prefix const &other) const
+	{
+		return prefix  != other.prefix ||
+		       address != other.address;
+	}
 };