Overlayfs should cope with online changes to underlying layer
without crashing the kernel, which is what xfstest overlay/019
checks.

This test may sometimes trigger WARN_ON() in ovl_create_or_link()
when linking an overlay inode that has been changed on underlying
layer.

Remove those WARN_ON() to prevent the stress test from failing.
Signed-off-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>