geneve: fix fill_info when using collect_metadata

Since 9b4437a5 ("geneve: Unify LWT and netdev handling.") fill_info
does not return UDP_ZERO_CSUM6_RX when using COLLECT_METADATA. This is
because it uses ip_tunnel_info_af() with the device level info, which is
not valid for COLLECT_METADATA.

Fix by checking for the presence of the actual sockets.

Fixes: 9b4437a5 ("geneve: Unify LWT and netdev handling.")
Signed-off-by: Eric Garver <e@erig.me>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>