NFS: Ensure the server has an up to date ctime before hardlinking

NFS: Ensure the server has an up to date ctime before hardlinking

BugLink: https://bugs.launchpad.net/bugs/1959879
[ Upstream commit 204975036b34f55237bc44c8a302a88468ef21b5 ]

Creating a hard link is required by POSIX to update the file ctime, so
ensure that the file data is synced to disk so that we don't clobber the
updated ctime by writing back after creating the hard link.

Fixes: 9f7682728728 ("NFS: Move the delegation return down into nfs4_proc_link()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>