The existing implementation wouldn't wake the connection cleaner if
maxIdleTime was set to a value less than maxLifetime while an existing
connection was open - resulting in idle connections not being discarded
until after the first maxLifetime had passed.

Fixes #45993

Change-Id: I074ed7ba9803354c8b3a41f2625ae0d8a7d5059b
GitHub-Last-Rev: 0d149d8d38bc9c2ad42a2a20dcfc73994d54fe23
GitHub-Pull-Request: golang/go#58490
Reviewed-on: https://go-review.googlesource.com/c/go/+/467655


Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>