Mark nodes that correspond to nodes that didn't decrypt a traceroute

[ianmcorvidae]

meshtastic/firmware#4056 is only just merged, but will mean that (once nodes are updated, and all that), nodes along a traceroute path that don't decrypt the packet and therefore don't add themselves to that path will show up as 0xFFFFFFFF when detected by a later node along the path. these should appear as unknown nodes already, but they should be distinguished in the traceroute display so it's known when a hop doesn't share a channel or is an ALL_SKIP_DECODING repeater. Additionally, during the period of time where nodes after a missing hop may still not have recent enough firmware for that PR, these dummy nodes can in theory be added to the path in a spot later than their actual location in the path, since they'll be added just before the first node past the missing hop in the chain, that has recent enough firmware, which makes it beneficial to identify them specifically compared to "regular" unknown nodes.