[CIFS] CIFS currently allows for permissions to be changed on files, even

[CIFS] CIFS currently allows for permissions to be changed on files, even
when unix extensions and cifsacl support are disabled. These
permissions changes are "ephemeral" however. They are lost whenever
a share is mounted and unmounted, or when memory pressure forces
the inode out of the cache.

Because of this, we'd like to introduce a behavior change to make
CIFS behave more like local DOS/Windows filesystems. When unix
extensions and cifsacl support aren't enabled, then don't silently
ignore changes to permission bits that can't be reflected on the
server.

Still, there may be people relying on the current behavior for
certain applications. This patch adds a new "dynperm" (and a
corresponding "nodynperm") mount option that will be intended
to make the client fall back to legacy behavior when setting
these modes.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>