BUG/MINOR: peers: Missing TX cache entries reset.

BUG/MINOR: peers: Missing TX cache entries reset.

The TX part of a cache for a dictionary is made of an reserved array of ebtree nodes
which are pointers to dictionary entries. So when we flush the TX part of such a
cache, we must not only remove these nodes to dictionary entries from their ebtree.
We must also reset their values. Furthermore, the LRU key and the last lookup
result must also be reset.

(cherry picked from commit ea875e62e6b2f69c50533c5cd52eb5284c69723f)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>