MINOR: stream: report the current rule in "show sess all" when known

MINOR: stream: report the current rule in "show sess all" when known

Sometimes an HTTP or TCP rule may take time to complete because it is
waiting for external data (e.g. "wait-for-body", "do-resolve"), and it
can be useful to report the action and the location of that rule in
"show sess all". Here for streams blocked on such a rule, there will
now be a "current_line" extra line reporting this. Note that this does
not catch rulesets which are re-evaluated from the start on each change
(e.g. tcp-request content waiting for changes) but only when a specific
rule is being paused.