datapath-windows: Support for multiple VXLAN tunnels

datapath-windows: Support for multiple VXLAN tunnels

At the moment the OVS extension supports only one VXLAN tunnel that
is cached in the extension switch context. Replaced the latter
cached pointer with an array list that contains all VXLAN tunnel
vports.

Signed-off-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Reported-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/64
Acked-by: Eitan Eliahu <eliahue@vmware.com>
Acked-by: Nithin Raju <nithin@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>