SELinux: Use unknown perm handling to handle unknown netlink msg types

Currently when SELinux has not been updated to handle a netlink message
type the operation is denied with EINVAL.  This patch will leave the
audit/warning message so things get fixed but if policy chose to allow
unknowns this will allow the netlink operation.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/hooks.c

@@ -4395,7 +4395,7 @@ static int selinux_nlmsg_perm(struct sock *sk, struct sk_buff *skb)
 				  "SELinux:  unrecognized netlink message"
 				  " type=%hu for sclass=%hu\n",
 				  nlh->nlmsg_type, isec->sclass);
-			if (!selinux_enforcing)
+			if (!selinux_enforcing || security_get_allow_unknown())
 				err = 0;
 		}