BACKPORT: Smack: Ptrace access check mode

BACKPORT: Smack: Ptrace access check mode

When the ptrace security hooks were split the addition of
a mode parameter was not taken advantage of in the Smack
ptrace access check. This changes the access check from
always looking for read and write access to using the
passed mode. This will make use of /proc much happier.

Targeted for git://git.gitorious.org/smack-next/kernel.git

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
(cherry-picked from upstream b5dfd8075bc26636d11c3d8888940198afbf5112)