Add netif_subqueue_completed_wake, complementing the subqueue versions
netif_subqueue_try_stop and netif_subqueue_maybe_stop.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>