Smack: adds smackfs/ptrace interface

Smack: adds smackfs/ptrace interface

This allows to limit ptrace beyond the regular smack access rules.
It adds a smackfs/ptrace interface that allows smack to be configured
to require equal smack labels for PTRACE_MODE_ATTACH access.
See the changes in Documentation/security/Smack.txt below for details.

Change-Id: If5d887a86b8d05ac46c82e1e7e123b86a5d62ddb
Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@partner.samsung.com>
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>
(cherry picked from commit a83c54f6fe32465181f24483f1f34685ad5a2466)

Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>