node-neigh: Fix obsolete nextHop removal

The impact of the wrong removal was very small - unnecessary neigh
insert via netlink and dangling unused value. This could have happened
under very rare circumstances when a next hop to a node had changed.

Fixes: 0483ba0 ("node-neigh: Do not inc neighbor refcount for the same node")
Signed-off-by: Martynas Pumputis <m@lambda.lt>

pkg/datapath/linux/node.go

@@ -719,7 +719,7 @@ func (n *linuxNodeHandler) insertNeighbor(ctx context.Context, newNode *nodeType
 						logfields.LinkIndex:    neigh.LinkIndex,
 					}).WithError(err).Info("Unable to remove neighbor entry")
 				}
-				delete(n.neighByNextHop, nextHopStr)
+				delete(n.neighByNextHop, existingNextHopStr)
 				delete(n.neighLastPingByNextHop, existingNextHopStr)
 				if option.Config.NodePortHairpin {
 					neighborsmap.NeighRetire(net.ParseIP(existingNextHopStr))