BUG/MEDIUM: cache: always verify the primary hash in get_secondary_entry()

BUG/MEDIUM: cache: always verify the primary hash in get_secondary_entry()

When checking for secondary entries, the tree is walked within duplicates
of the primary key, only indexed on the first 32 bits, which means that
in case of hash collision, we could start looking for an object and
switch to another one while visiting secondaries. In order to avoid this
we simply need to always check the full primary hash of the entry that
was found.

This should be backported to all stable versions.