fix(perf): run iperf on TCP and set TCP windows to bdp (#241)

This commit makes iperf use TCP instead of UDP. Using UDP allows the sender to
send as much data as they can, not as much data as the receiver can handle.
Using TCP measures the actual bandwidth of the connection.

This commit sets the TCP send and receive window to the bandwidth-delay-product.
In order to exhaust the whole bandwidth between the two nodes, TCP needs to be
able to buffer all bytes on the wire in the case of packet loss.