watchfs: treesize propagation issues

[rhafer]

Describe the bug

When updating or deleting files on a watchfs-enabled system the treesize changes are not propagated correctlys

Steps to reproduce

Inside the space root of a personal space do:

# xattr -p user.oc.treesize .
0
# echo 1234567890 > test.txt
# xattr -p user.oc.treesize .
11
# echo 12345 > test.txt
# xattr -p user.oc.treesize .
11
# rm test.txt
# xattr -p user.oc.treesize .
11

[rhafer]

@aduffeck Here's the bug report for the treesize issue. Just for completeness.