QNAP Manila driver: the size of share/snapshot is inconsistent with NAS while create/manage from snapshot

There are two situation may cause the size of share/snapshot managed by manila is inconsistent with the NAS backend.

One is to create a share from snapshot.

Step to reproduce:
(Create share from snapshot)
1. Create a share with 5GB size

2. Take a snapshot of this share

3. Extend this share to 10GB size

4. Create a share from this snapshot

Expect:

Create a share from snapshot with 5GB size.

Result:

The NAS backend will create a share with 10GB size due to lack of size parameter.

While the other one is manage an existing snapshot.

Step to reproduce:
(Manage existing snapshot)

1. Create a share with 5GB size

2. Take a snapshot of this share on NAS backend

3. Extend the share to 10GB size

4. Manage this snapshot

Expect:

The managed snapshot size is 5GB.

Result:
Due to the lack of snapshot size, manila use share size instead. The managed snapshot size will be 10GB.