Description of problem:
Incremental sync results in nonidentical source and destination snapshots for:
1. Incremental Syncing of already existing snapshots.
2. test_cephfs_mirror_incremental_sync in qa/tasks/cephfs/test_mirroring.py.

Version-Release number of selected component (if applicable):
8.1

How reproducible:
Intermittently. 
These issues are not always reproducible.

Steps to Reproduce:
1.
Incremental Syncing of already existing snapshots
-------------------------------------

Mount:
```
$ sudo ./bin/mount.ceph admin@.a=/ /mnt/cephfs1 -o conf=$(pwd)/ceph.conf;
$ sudo ./bin/mount.ceph admin@.remotefs=/ /mnt/cephfs2 -o conf=$(pwd)/ceph.conf;
```

Make some changes and take a snapshot:
```
$ mkdir -p /mnt/cephfs1/dir/d1
$ touch /mnt/cephfs1/dir/d1/file1
$ mkdir -p /mnt/cephfs1/dir/.snap/snap1; 
```

Make some more changes & take another snapshot:
```
$ touch /mnt/cephfs1/dir/d1/file2
$ mkdir -p /mnt/cephfs1/dir/.snap/snap2;
```

Make a change and don't take snapshot:
`
$ rm /mnt/cephfs1/dir/d1/file2
`

Add `dir` for mirroring:
`
$ ./bin/ceph fs snapshot mirror add a /dir
`

Results:
```
$ tree /mnt/cephfs1/dir/.snap
/mnt/cephfs1/dir/.snap
├── snap1
│   └── d1
│       └── file1
└── snap2
    └── d1
        ├── file1
        └── file2
```

```
$ tree /mnt/cephfs2/dir/.snap
/mnt/cephfs2/dir/.snap
├── snap1
│   └── d1
│       └── file1
└── snap2
    └── d1
        └── file1
```

```
$ tree /mnt/cephfs1/dir
/mnt/cephfs1/dir
└── d1
    └── file1
```

```
$ tree /mnt/cephfs2/dir
/mnt/cephfs2/dir
└── d1
    └── file1
```

2.
test_cephfs_mirror_incremental_sync in qa/tasks/cephfs/test_mirroring.py:
------------------------------------------------------------------------
The steps of test_cephfs_mirror_incremental_sync produces nonidentical source and destination snapshots after incremental sync of a repo (with .git directory). The checksum of .git directory differs.

Actual results:
1.
In the above example, /mnt/cephfs1/dir/.snap/snap2 and /mnt/cephfs2/dir/.snap/snap2 are different which is a bug.

2.
Incremental sync of a repo produces nonidentical source and destination snapshots.

Expected results:
1.
/mnt/cephfs1/dir/.snap/snap2 and /mnt/cephfs2/dir/.snap/snap2 should be identical.

2.
Incremental sync of a repo should produce identical source and destination snapshots.

Additional info: