fix: improve mount quota enforcement to prevent overflow (#7804)

* fix: improve mount quota enforcement to prevent overflow (fixes seaweedfs-csi-driver#218)

* test: add unit tests for quota enforcement

weed/mount/weedfs_link.go

@@ -25,7 +25,7 @@ When creating a link:
 
 /** Create a hard link to a file */
 func (wfs *WFS) Link(cancel <-chan struct{}, in *fuse.LinkIn, name string, out *fuse.EntryOut) (code fuse.Status) {
-	if wfs.IsOverQuota {
+	if wfs.IsOverQuotaWithUncommitted() {
 		return fuse.Status(syscall.ENOSPC)
 	}