check: mnt_id is now in mainline
check: mnt_id is now in mainline

As of
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=49d063cb3
the mnt_id field is in mainline, so let's check for it in --ms.

Signed-off-by: Tycho Andersen <10c18fcb898ee6b17d6575d444b125d10b3f4d6a@canonical.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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