MINOR: stream: maintain per-stream counters of the number of passes on code

MINOR: stream: maintain per-stream counters of the number of passes on code

Process_stream() is a complex function and a few times some lopos were
either witnessed or suspected. Each time this happens it's extremely
difficult to figure why because it involves combinations of analysers,
filters, errors etc.

Let's at least maintain a set of 4 counters per stream that report the
number of times we've been through each of the 4 most important blocks
(stconn changes, request analysers, response analysers, and propagation
of changes down). These ones are stored in the stream and reported in
"show sess all", just like they will be reported in panic dumps.