drbd: fix resend/resubmit of frozen IO

DRBD can freeze IO, due to fencing policy (fencing resource-and-stonith),
or because we lost access to data (on-no-data-accessible suspend-io).

Resuming from there (re-connect, or re-attach, or explicit admin
intervention) should "just work".

Unfortunately, if the re-attach/re-connect did not happen within
the timeout, since the commit
  drbd: Implemented real timeout checking for request processing time
if so configured, the request_timer_fn() would timeout and
detach/disconnect virtually immediately.

This change tracks the most recent attach and connect, and does not
timeout within <configured timeout interval> after attach/connect.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>