Reverting to old negative_caching conditional behavior (#7401)

https://github.com/apache/trafficserver/pull/7361 fixed negative caching
for non-cacheable negative responses, but it broke certain logic
concerning checks for whether a given response was cacheable because of
negative caching configuration. This fixes the latter behavior so it now
behaves as it did before.

Co-authored-by: bneradt <bneradt@verizonmedia.com>
3 files changed