mounts: mntns_collect_root in __open_mountpoint
mounts: mntns_collect_root in __open_mountpoint

We are going to support nested mount namespaces,
file descriptors can be from different namespaces,
so a namespace root must be updated for each of them.

Signed-off-by: Andrey Vagin <74c05afa918858348d6db8037d82fa8124870113@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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