cifs mount regression in 4.8 and 4.4 stable

[Seth Forshee]

We've received reports from users of a cifs mount regression in our
4.4-based kernel, e.g. [1]. It is fixed by reverting the follwing commit
from 4.8 which was applied to 4.4 stable:

 a6b5058 fs/cifs: make share unaccessible at root level mountable

Testing against 4.8-rc7 shows that the problem is present there as well.

Thanks,
Seth

[1] http://bugs.launchpad.net/bugs/1626112