setAttr left attr.Ino unset (0) and the NewInode sites left StableAttr.Ino
unset, so the kernel saw inode 0 while the node identity differed, which
breaks NFS file-handle validation. Set both to the stable VFS inode. The
bazil cmd/mount backend does not hit this because its framework assigns
stable inodes automatically; go-fuse needs them set explicitly.
Before: chmod/chown/truncate on a just-written file through an
NFS-exported mount2 mount failed with ESTALE.
After: they succeed.
Exercising the NFS handle-validation path needs a kernel NFS server, so it
isn't covered by the local vfstest harness; validated against a real Linux
nfs-kernel-server export over NFSv3, NFSv4.0 and NFSv4.2.
#9547
(cherry picked from commit 92b78aefa4)
b9fd40d182