vpp-manager: Add static neighbor for LL address on tap0

This patch adds a static neighbor for the node's LinkLocal
address on tap0. This simplify things as we know the node's
link local in advance and use it for other purposes, so we
save a resolution. Also we do not yet support it changing.

Finally if we do not have this, we learn the neighbor through
gratuitous requests from linux to ND proxy and NS/ND, but as
we do not have a glean toward linux, we cannot learn the neighbor
if packets are coming from the uplink without prior linux
initiated sollicits. As an example DHCPv6 sollicts replies
need forwarding and we might have forgotten the neighbor by then.

Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>

Author: sknat

vpp-manager/vpp_runner.go

@@ -224,9 +224,18 @@ func (v *VppRunner) configureIPv6LinkLocal(ifSpec *config.UplinkInterfaceSpec, i
 		ifSpec.InterfaceName, *config.GetCalicoVppDebug().FetchV6LLntries)
 
 found:
+	err := v.vpp.AddNeighbor(&types.Neighbor{
+		SwIfIndex:    ifState.TapSwIfIndex,
+		IP:           ifState.IPv6LinkLocal.IP,
+		HardwareAddr: ifState.HardwareAddr,
+		Flags:        types.IPNeighborStatic,
+	})
+	if err != nil {
+		return errors.Wrapf(err, "error add static neighbor for %s tap0 %d", ifState.IPv6LinkLocal.IP, ifState.TapSwIfIndex)
+	}
 	// Add LL /128 route to punt table so that punted link-local traffic
 	// reaches the host via tap instead of hitting fe80::/10 → ip6-link-local.
-	err := v.vpp.RouteAdd(&types.Route{
+	err = v.vpp.RouteAdd(&types.Route{
 		Table: common.PuntTableID,
 		Dst:   common.FullyQualified(ifState.IPv6LinkLocal.IP),
 		Paths: []types.RoutePath{{