osd/scrub: uniform handling of reservation requests

osd/scrub: uniform handling of reservation requests

we now allow - on the replica side - reservation requests
regardless of the ReplicaActive sub-state. I.e. - we will
honor such requests even when handling a chunk request
(in ReplicaActiveOp).

Note that the current Primary code would never send such
a request. But a future primary code might.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>
(cherry picked from commit 005839bdd41835a3235af81c5b9a42f19b663686)