Limit number of remote requests

[prasimix]

We have to limit somehow number of remote requests over serial/USB and Ethernet to avoid erratic behavior or skipping of watchdog impulses that will shut PSU down.

[prasimix]

If long enough sequence of nonsensical text is send via serial to make error queue overflow that can initiate unrelated events such as false PWRGOOD detection and "trigger" DOUT2 relay.

[prasimix]

Fixed in a way that e.g. stream of "garbage" sent over communication port cannot push PSU into standby mode anymore (due to watchdog timeout). Malicious user still could stop for few seconds other functions (i.e. LIST executions, protection tripping).