Throughput reduced when routing to multiple targets

[evoggy]

When streaming images from the GAP8 the throughput is severely reduced when also sending messages from the STM32 to the GAP8 at the same time. It's unclear what part in the chain is causing this, but it's clear that the GAP8 seems that sending the images takes way longer, which could be caused by the ESP32 not handling the transactions fast enough.

First reported by @whoenig in this forum thread were there's firmware to reproduce the issue.

[evoggy]

This should be fixed in #11.

For unknown reasons the ESP RTT is suddenly not reset properly and after that it starts behaving strangely. The symptom of this is that the GAP8 RTT is ignored and ESP RTT will only go high (which starts the transaction) when communication is initiated from the ESP. In the example to reproduce this the ESP only sent data once per second, which means the GAP8 could only send data once per second. This drastically reduced the frame rate.