CRIU is preserving ifindexes of net devices after restoration. However,
current Open vSwitch API does not allow to target ifindex, so we cannot
correctly restore OVS configuration.

Add new OVS_DP_ATTR_IFINDEX for OVS_DP_CMD_NEW and use it as desired
ifindex.
Use OVS_VPORT_ATTR_IFINDEX during OVS_VPORT_CMD_NEW to specify new netdev
ifindex.

Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>