security_classes

Define new netlink socket security classes introduced by upstream kernel commit
6c6d2e9bde1c1c87a7ead806f8f5e2181d41a652 ("selinux: update netlink socket
classes").  This was merged in Linux 4.2 and is therefore only required
for Android kernels based on 4.2 or newer (e.g. the android-4.4 branch
of the kernel/common tree).

Add the new socket classes to socket_class_set.
Add an initial set of allow rules although further refinement
will likely be necessary.  Any allow rule previously written
on :netlink_socket may need to be rewritten or duplicated for
one or more of the more specific classes.  For now, we retain
the existing :netlink_socket rules for compatibility on older kernels.

Change-Id: I5040b30edd2d374538490a080feda96dd4bae5bf
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>