Fix the upload speed calculation (K/s indicator)

It should at least take multiple concurrent slots into account. Hypothetically, take someone with 10 slots. 9/10 slots are occupied by users with max breakneck speeds of 10kB/s. The 10th slot goes to a more fortunate person, that manages to fully saturate the rest of the uploader's bandwidth (DLing at 99910kB/s). The uploader's speed somehow ends up averaged as ~10000kB/s (in most fortunate cases! it can end up much lower) and not the full 100000kB/s they are realistically capable of.