Revert "ecryptfs: forbid opening files without mmap handler"

Revert "ecryptfs: forbid opening files without mmap handler"

This reverts commit 2f36db71009304b3f0b95afacd8eba1f9f046b87.

It fixed a local root exploit but also introduced a dependency on
the lower file system implementing an mmap operation just to open a file,
which is a bit of a heavy hammer.  The right fix is to have mmap depend
on the existence of the mmap handler instead.

Change-Id: I78753c9cadef7b43cd277d4827a096b45697c288
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Cc: stable@vger.kernel.org
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
Git-commit: 78c4e172412de5d0456dc00d2b34050aa0b683b5
Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>