selinux: Convert socket related access controls to use socket labels

At present, the socket related access controls use a mix of inode and
socket labels; while there should be no practical difference (they
_should_ always be the same), it makes the code more confusing.  This
patch attempts to convert all of the socket related access control
points (with the exception of some of the inode/fd based controls) to
use the socket's own label.  In the process, I also converted the
socket_has_perm() function to take a 'sock' argument instead of a
'socket' since that was adding a bit more overhead in some cases.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>