Unexpected exception traces are some times generated

[Viktor Vilhelm Sonesten]

When tracing a trimmed down blinky (where only app::toggle is expected to generate exception traces) some runs (reruns of cargo rtic-scope trace) yield unexpected exception traces. In this case only the exception SysTick is defined and explicitly used, but IRQ numbers of 128 and 23 are reported. Additionally, some times ThreadMode is also reported, but that should perphaps be expected.

ExceptionTrace { exception: Interrupt { irqn: 128 }, action: Entered }
ExceptionTrace { exception: ThreadMode, action: Returned }

No MWE at present.

[Viktor Vilhelm Sonesten]

This is not a RTIC Scope issue; it's up to the target if it sends us unexpected packets. We should handle and forward them to the sinks.