Return immediately from pdcp_data_req
When the RLC layer returns error codes (like dropped packets), this is still counted as PDCP layer traffic. In order to reflect dropped packets or malfunctioning, this patch makes that upon an RLC error code, the function is exited immediately. In this case, it is not counted as additional PDCP traffic. An example is too much UDP traffic. If the RLC buffer is saturated and the packet therefore refused, incoming traffic won't be counted anymore. With this patch, the PDCP layer statistics won't count such traffic anymore.