l2tp: set netnsok flag for netlink messages

The L2TP netlink code can run in namespaces.  Set the netnsok flag in
genl_family to true to reflect that fact.

Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_netlink.c

@@ -37,6 +37,7 @@ static struct genl_family l2tp_nl_family = {
 	.version	= L2TP_GENL_VERSION,
 	.hdrsize	= 0,
 	.maxattr	= L2TP_ATTR_MAX,
+	.netnsok	= true,
 };
 
 /* Accessed under genl lock */