Fix the request transition from linger -> normal request. The key is to
preserve r_osd and requeue on the same OSD. Reregister as a normal request,
add the request to the proper queues, then unregister the linger. Fix the
unregister helper to avoid clearing r_osd (and also simplify the parallel
check in __unregister_request()).
Reported-by: Henry Chang <henry.cy.chang@gmail.com> Signed-off-by: Sage Weil <sage@newdream.net>