BUG/MEDIUM: servers: Don't forget to set srv_hash when needed

BUG/MEDIUM: servers: Don't forget to set srv_hash when needed

Commit 8aa854ab26a7daa613a17548f1fe1d0adb8cf61b made it so we'd store
the hash corresponding to the server parameters, so that we could detect
if we're still talking to the same server, and not use those parameters
if not.
However, when updating those parameters, we forgot to store the new
hash, which would result in the new parameters never be used, and
breakling 0RTT.
Fix that by properly update the hash when needed.
This should be backported when 8aa854ab26a7daa613a17548f1fe1d0adb8cf61b
is backported.