openvswitch: do not ignore netdev errors when creating tunnel vports

The creation of a tunnel vport (geneve, gre, vxlan) brings up a
corresponding netdev, a multi-step operation which can fail.

For example, changing a vxlan vport's netdev state to 'up' binds the
vport's socket to a UDP port - if the binding fails (e.g. due to the
port being in use), the error is currently ignored giving the
appearance that the tunnel vport creation completed successfully.

Signed-off-by: Martynas Pumputis <martynas@weave.works>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>