libceph: bump CEPH_PG_MAX_SIZE to 32

... to accommodate potentially very wide EC pools.  This increases the
size of a typical rbd ceph_osd_request by ~12% (from 1040 to 1168 bytes),
but I'd rather go future proof here.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

include/linux/ceph/rados.h

@@ -50,7 +50,7 @@ struct ceph_timespec {
 #define CEPH_PG_LAYOUT_LINEAR 2
 #define CEPH_PG_LAYOUT_HYBRID 3
 
-#define CEPH_PG_MAX_SIZE      16  /* max # osds in a single pg */
+#define CEPH_PG_MAX_SIZE      32  /* max # osds in a single pg */
 
 /*
  * placement group.