net: Fix netns for ip_tunnel_init_flow()

The device denoted by tunnel->parms.link resides in the underlay net
namespace. Therefore pass tunnel->net to ip_tunnel_init_flow().

Fixes: db53cd3d ("net: Handle l3mdev in ip_tunnel_init_flow")
Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20241219130336.103839-1-shaw.leon@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>