ovl: store and show the user provided lowerdir mount option

ovl: store and show the user provided lowerdir mount option

[ Upstream commit 0cea4c097d97fdc89de488bd4202d0b087ccec58 ]

We are about to add new mount options for adding lowerdir one by one,
but those mount options will not support escaping.

For the existing case, where lowerdir mount option is provided as a colon
separated list, store the user provided (possibly escaped) string and
display it as is when showing the lowerdir mount option.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Stable-dep-of: 2824083db76c ("ovl: Always reject mounting over case-insensitive directories")
Signed-off-by: Sasha Levin <sashal@kernel.org>