Store reserved offers in a Set instead

ReservedOffers should be identified by the reservationId, not the
requestId. Furthermore, a reserved offer can be torn down outside of
onNetworkUnneeded() at which point there is not request to reference.

This change replaces the Map of requestId -> reservedOffer to a Set of
reservedOffers.

Test: TH
Change-Id: I622c86fe238b2412664add55ce491eb5baf6033f
1 file changed