net, ip_tunnel: fix namespaces move

in the same manner as commit 690afc16 ("net: ip6_gre: fix moving
ip6gre between namespaces"), fix namespace moving as it was broken since
commit 2e15ea39 ("ip_gre: Add support to collect tunnel metadata.").
Indeed, the ip6_gre commit removed the local flag for collect_md
condition, so there is no reason to keep it for ip_gre/ip_tunnel.

this patch will fix both ip_tunnel and ip_gre modules.

Fixes: 2e15ea39 ("ip_gre: Add support to collect tunnel metadata.")
Signed-off-by: William Dauchy <w.dauchy@criteo.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>