CRED: Wrap task credential accesses in the IPv6 protocol

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: netdev@vger.kernel.org
Signed-off-by: James Morris <jmorris@namei.org>

net/ipv6/ip6_flowlabel.c

@@ -388,7 +388,7 @@ fl_create(struct net *net, struct in6_flowlabel_req *freq, char __user *optval,
 		fl->owner = current->pid;
 		break;
 	case IPV6_FL_S_USER:
-		fl->owner = current->euid;
+		fl->owner = current_euid();
 		break;
 	default:
 		err = -EINVAL;