[GRE]: Allow for IPPROTO_GRE protocol in namespaces.

This one was also disabled by default for sanity.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 7ff5262..2ada033 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -1297,6 +1297,7 @@
 static struct net_protocol ipgre_protocol = {
 	.handler	=	ipgre_rcv,
 	.err_handler	=	ipgre_err,
+	.netns_ok	=	1,
 };
 
 static void ipgre_destroy_tunnels(struct ipgre_net *ign)