BUG/MEDIUM: bwlim: Be sure to never set the analyze expiration date in past

BUG/MEDIUM: bwlim: Be sure to never set the analyze expiration date in past

Every time a bandwidth limitation is evaluated on a channel, the analyze
expiration date is renewed, mainly based on the internal bandwidth
limitation filter expiration date. However, when the filter is called while
there is no data to filter, we skip all limitation computations to jump at
the end of the function. At this stage, the analyze expiration date is
renewed before exiting. But here the internal expiration date may be expired
and not reset.

To sum up, it is possible to set the analyze expiration date of a channel in
the past. It is unexpected and this could lead to a loop in process_stream.

To fix the issue, we just now take care to reset the internal expiration
date, if needed, before exiting.

This patch should fix the issue #2634. It must be backported as far as 2.8.