selinux: fix a problem with IPv6 traffic denials in selinux_ip_postroute()

A previous commit c0828e50 ("selinux:
process labeled IPsec TCP SYN-ACK packets properly in
selinux_ip_postroute()") mistakenly left out a 'break' from a switch
statement which caused problems with IPv6 traffic.

Thanks to Florian Westphal for reporting and debugging the issue.
Reported-by: Florian Westphal <fwestpha@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

security/selinux/hooks.c

@@ -4993,6 +4993,7 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
 			case PF_INET6:
 				if (IP6CB(skb)->flags & IP6SKB_XFRM_TRANSFORMED)
 					return NF_ACCEPT;
+				break;
 			default:
 				return NF_DROP_ERR(-ECONNREFUSED);
 			}