DEBUG: stream: Display the currently running rule in stream dump

DEBUG: stream: Display the currently running rule in stream dump

Since the 2.5, when stream's info are dump, it is possible to print the
yielding rule, if any. It was useful to detect buggy rules on spinning
loop. But it is not possible to detect a rule consuming too much CPU
per-execution. We can see a rule was executing in the backtrace reported by
the watchdog, but we are unable to spot the specific rule.

Thanks to this patch, it is now possible. When a dump is emitted, the
running or yield rule is now displayed with its current state (RUNNING or
YIELDING).

This patch could be backported as far as 3.2 because it could be useful to
spot issues.