cleanup MAC PDU generation (plus some general cleanup)
The code was very unclear and potentially buggy. This new version is more robust. We can waste up to 2 bytes because the last header in the MAC PDU does not contain a length field and when we request data from RLC we suppose a 3-bytes MAC header. This might be optimized at some point, but the benefit would be low. This commit also contains some general cleanup: - formatting - variables' types: let's use 'int' instead of trying to be clever by using small types that may generate bugs if the value is too big - remove 'tpc_accumulated' which was globally used for all UEs and has no purpose other than logging. We may want to rework a bit the TPC machinery at some point. As the code is today we may repeatedly send TPC over and over without caring about the 3GPP limits, in which case no one knows how the UE is supposed to behave: does it clamp the current max value or does it accumulate over and over and take the clamped value to compute its actual power? If we send a reverse TPC (reduce power instead of increase) does it do it immediately or does it have to decrease n+1 times if we previously ordered it to increase n times?) We do not address the problem of prioritizing LCIDs. As of today there is only one dedicated traffic channel (DTCH), so it's not a problem at this point. What has been tested: - monolithic eNB 5/10/20MHz with one cots UE, TCP/UDP UL/DL. At 20MHz the machine used was not capable of keeping up, generating lots of Us and Ls when the throughput reaches 60Mb/s. USRP B210 was used.