Merge r1572630, r1572611, r1572967, r1573229 from trunk:
Redo what was reverted in r1572627. Don't reuse a SSL backend connection whose SNI differs. PR 55782. This may happen when ProxyPreserveHost is on and the proxy-worker handles connections to different Hosts.
Follows up r1572606. MMN minor bump required by proxy_conn_rec change.
mod_proxy: follows up r1572630. Don't reuse a SSL backend connection with no SNI for a request requiring SNI.
mod_proxy: Add comment and avoid ternary operator as condition (no functional change). Submitted by: ylavic Reviewed/backported by: jim