UBUNTU: SAUCE: apparmor: fix cross ns perm of unix domain sockets

UBUNTU: SAUCE: apparmor: fix cross ns perm of unix domain sockets

When using nested namespaces policy within the nested namespace is trying
to cross validate with policy outside of the namespace that is not
visible to it. This results the access being denied and with no way to
add a rule to policy that would allow it.

The check should only be done again policy that is visible.

BugLink: http://bugs.launchpad.net/bugs/1660832
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>