Implement exponential backoff in vrf plugin

The current max waiting time for global IPV6 addresses
to be present in the kernel after reinserting them is not
sufficient for all use cases. SRIOV + VRF takes around 1.2s.

These changes increase the maximum waiting time to approximately
2.5s. An exponential backoff is implemented to reduce cpu overload.

Signed-off-by: Marcelo Guerrero <marguerr@redhat.com>

Author: Marcelo Guerrero

plugins/meta/vrf/vrf.go

@@ -154,8 +154,9 @@ CONTINUE:
 		}
 
 		// Waits for global IPV6 addresses to be added by the kernel.
-		maxRetry := 10
-		for {
+		backoffBase := 10 * time.Millisecond
+		maxRetries := 8
+		for retryCount := 0; retryCount <= maxRetries; retryCount++ {
 			routesVRFTable, err := netlink.RouteListFiltered(
 				netlink.FAMILY_ALL,
 				&netlink.Route{
@@ -176,12 +177,13 @@ CONTINUE:
 				break
 			}
 
-			maxRetry--
-			if maxRetry <= 0 {
+			if retryCount == maxRetries {
 				return fmt.Errorf("failed getting local/host addresses for %s in table %d with dst %s", intf, vrf.Table, toFind.IPNet.String())
 			}
 
-			time.Sleep(10 * time.Millisecond)
+			// Exponential backoff - 10ms, 20m, 40ms, 80ms, 160ms, 320ms, 640ms, 1280ms
+			// Approx 2,5 seconds total
+			time.Sleep(backoffBase * time.Duration(1<<retryCount))
 		}
 	}