apparmor: fix blob compression when ns is forced on a policy load

When blob compression is turned on, if the policy namespace is forced
onto a policy load, the policy load will fail as the namespace name
being referenced is inside the compressed policy blob, resulting in
invalid or names that are too long. So duplicate the name before the
blob is compressed.

Fixes: 876dd866c084 ("apparmor: Initial implementation of raw policy blob compression")
Signed-off-by: John Johansen <john.johansen@canonical.com>