osd: don't clobber racing pg_info on active pg
osd: don't clobber racing pg_info on active pg

Wido saw a pg go active, but an activate log+info update crossed paths with
a pg_notify info, and the primary overwrote it's updated shiny new info
with the stale old info from the replica.  Don't do that.  It causes
problems down the line.  In this case, we got

osd/OSD.cc: In function 'void OSD::generate_backlog(PG*)':
osd/OSD.cc:3863: FAILED assert(!pg->is_active())
 1: (ThreadPool::worker()+0x28f) [0x5b08ff]
 2: (ThreadPool::WorkThread::entry()+0xd) [0x4edb8d]
 3: (Thread::_entry_func(void*)+0xa) [0x46892a]
 4: (()+0x69ca) [0x7f889ff249ca]
 5: (clone()+0x6d) [0x7f889f1446cd]

on the replica because it was active but the primary was restarting peering
due to the bad info.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph