Track how many ntor/tap cells we received/processed

As part of #9574 (moved) Mike suggested that we make relays report how many TAP and NTor circuit-level handshakes they see.

This data would be most useful if we report "number received" and "number processed" for each one, so we can track both sides of the trends.

I'm not sure if we'll want this in 0.2.4 or 0.2.5 -- it would sure be useful to have it in 0.2.4 along with #9574 (moved), but it will depend how klunky the patch is.