Lte uses RLC TM for application data

When using TCP + LTE, I found that RLC UM is introducing additional reordering delays (while the reordering should be done at TCP level). So, I wanted to use RLC TM, but it was not possible (and the first commit fixes that). Then, I discovered that TM sends only one packet per transmission opportunity, without considering how big is this transmission opportunity. The second patch fixes that.

Now, I am not sure what implications it may have on the control messages, but for what regards data packets, be able to use LTE TM with TCP is a huge improvement.