Detect zombie connections

[s-allius]

Especially the GEN3 inverters hold a TCP connection, but didn't send data anymore.

We want to detect dead connection on which we didn't receive a packet for a long time and disconnect this connection. Hopefully the inverter will establish a new connection and we will get data again.

For GEN3 inverters:
There is no heartbeat and the inverter sends data every 300sec. So the timeout should 7 to 10min

For GEN3PLUS inverters:
They have a heartbeat which sends a packet every minute. Here the timeout should be 2 or 3 minutes.

[s-allius]

fixed by #101