hierarchy stats: Only increment the total packet count once per frame

The same hierarchy of protocols can appear multiple times in a frame, for example if there are multiple PDUs for a protocol that begin in that frame. Keep track of the last frame where we incremented our stat node and use that to only increment it once per frame.

Add "total number of PDUs with this hierarchy" statistic and column that has the old value.

In the purpose of doing this, get rid of temporary variables and increment the ph_stats_t members directly, since we pass that into our functions already, and thus have access to the current packet count.

Fix #17553 (closed). Fix #18034 (closed). Fix #12565 (closed).