mds: relax divergent backtrace scrub failures for replicated ancestor inodes

mds: relax divergent backtrace scrub failures for replicated ancestor inodes

scrub could be verifying backtrace for an inode for which some of its
ancestors might be replicas, e.g. (from a custom debug build) some
ancestors of an inode with divergent backtrace were replicas:

```
[inode 0x3000000502f [...122,head] /volumes/qa/sv_0/b98de6ea-ed40-40d0-8e1a-9433a337a387/client.0/tmp/payload.2/multiple_rsync_payload.190107/firmware/ rep@0.1 fragtree_t(*^3) v6663 f(v493 m2024-05-01T06:38:16.403080+0000 388=289+99) n(v139 rc2024-05-01T06:55:35.239345+0000 b467915716 4880=4534+346) old_inodes=24 (inest mix) (ifile mix) | lock=0 importing=0 dirfrag=1 0x55a85d244680]
```

In such cases, the backpointer version (inode_backpointer_t::version) of the
in-memory (cache) inode can fall behind the on-disk version causing scrub to
consider the inode backtrace as divergent (memory version < on-disk version).

Sample:

```
"ondisk_value":"(2)0x30000005bba:

[<0x3000000502f/mwl8k v2126>,
<0x30000005026/firmware v6663>,
<0x30000005025/multiple_rsync_payload.190107 v3041>,
<0x10000005894/payload.2 v4873>,
<0x10000000005/tmp v6193>,<0x10000000003/client.0 v5964>,
<0x10000000002/b98de6ea-ed40-40d0-8e1a-9433a337a387 v5817>
,<0x10000000001/sv_0 v5837>,
<0x10000000000/qa v6241>,
<0x1/volumes v4036>]

"memoryvalue":"(2)0x30000005bba:

[<0x3000000502f/mwl8k v2126>,
<0x30000005026/firmware v6663>,
<0x30000005025/multiple_rsync_payload.190107 v3041>,
<0x10000005894/payload.2 v4873>,
<0x10000000005/tmp v6081>,
<0x10000000003/client.0 v5942>,
<0x10000000002/b98de6ea-ed40-40d0-8e1a-9433a337a387 v5709>,
<0x10000000001/sv_0 v5819>,
<0x10000000000/qa v6121>,
<0x1/volumes v4022>]
```

Fixes: http://tracker.ceph.com/issues/64730
Signed-off-by: Venky Shankar <vshankar@redhat.com>
(cherry picked from commit b98bb860a899ba86caf2d0e4d82b5882a13ae840)