mnt: Factor umount_mnt from umount_tree
mnt: Factor umount_mnt from umount_tree

For future use factor out a function umount_mnt from umount_tree.
This function unhashes a mount and remembers where the mount
was mounted so that eventually when the code makes it to a
sleeping context the mountpoint can be dput.

Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <8a741aa8cbd77ebc4a56ddb528ce9fd15d42f034@xmission.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs