Summary:
After releasing a snapshot, it checks whether it is suitable to trigger bottom compactions.
When disabling auto compactions, it may still schedule compaction when releasing a snapshot. Whereas no compaction job will be actually handled, so the state of LSM is not changed and compaction will be triggered again and again every time releasing a snapshot.

Too frequent compactions lead to high CPU usage and high db_mutex lock contention which affects foreground write duration finally.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7267

Test Plan:
- make check
- manual test

Reviewed By: akankshamahajan15

Differential Revision: D23252880

Pulled By: ajkr

fbshipit-source-id: 4431e071a35d9912a2a3592875db27bae521434b