user_ns: target af_key capability check

This presumes that it really is complete wrt network namespaces.  Looking
at the code it appears to be.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/net/key/af_key.c b/net/key/af_key.c
index 1e733e9..1f90f4e 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -141,7 +141,7 @@
 	struct sock *sk;
 	int err;
 
-	if (!capable(CAP_NET_ADMIN))
+	if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
 		return -EPERM;
 	if (sock->type != SOCK_RAW)
 		return -ESOCKTNOSUPPORT;