[SECMARK]: Add SELinux exports

Add and export new functions to the in-kernel SELinux API in support of the
new secmark-based packet controls.

Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>