libnet/d/bridge: dead code: no conflict on stale default nw

A check was added to the bridge driver to detect when it was called to
create the default bridge nw whereas a stale default bridge already
existed. In such case, the bridge driver was deleting the stale network
before re-creating it. This check was introduced in docker/libnetwork@6b158eac6a4877c27828f524ad1ca0ea4bd2a789
to fix an issue related to newly introduced live-restore.

However, since commit docker/docker@ecffb6d58cf89371e3f4a20f55c2e614dbdfe880,
the daemon doesn't even try to create default networks if there're
active sandboxes (ie. due to live-restore).

Thus, now it's impossible for the default bridge network to be stale and
to exists when the driver's CreateNetwork() method is called. As such,
the check introduced in the first commit mentioned above is dead code
and can be safely removed.

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

libnetwork/drivers/bridge/bridge_linux.go

diff --git a/libnetwork/drivers/bridge/bridge_linux.go b/libnetwork/drivers/bridge/bridge_linux.go
index 700a0e7..005c726 100644
--- a/libnetwork/drivers/bridge/bridge_linux.go
+++ b/libnetwork/drivers/bridge/bridge_linux.go
@@ -42,14 +42,6 @@
 	DefaultGatewayV6AuxKey = "DefaultGatewayIPv6"
 )
 
-type defaultBridgeNetworkConflict struct {
-	ID string
-}
-
-func (d defaultBridgeNetworkConflict) Error() string {
-	return fmt.Sprintf("Stale default bridge network %s", d.ID)
-}
-
 type (
 	iptableCleanFunc   func() error
 	iptablesCleanFuncs []iptableCleanFunc
@@ -674,15 +666,7 @@
 
 	// check network conflicts
 	if err = d.checkConflict(config); err != nil {
-		nerr, ok := err.(defaultBridgeNetworkConflict)
-		if !ok {
-			return err
-		}
-		// Got a conflict with a stale default network, clean that up and continue
-		log.G(context.TODO()).Warn(nerr)
-		if err := d.deleteNetwork(nerr.ID); err != nil {
-			log.G(context.TODO()).WithError(err).Debug("Error while cleaning up network on conflict")
-		}
+		return err
 	}
 
 	// there is no conflict, now create the network
@@ -700,15 +684,6 @@
 		nwConfig := nw.config
 		nw.Unlock()
 		if err := nwConfig.Conflicts(config); err != nil {
-			if nwConfig.DefaultBridge {
-				// We encountered and identified a stale default network
-				// We must delete it as libnetwork is the source of truth
-				// The default network being created must be the only one
-				// This can happen only from docker 1.12 on ward
-				log.G(context.TODO()).Infof("Found stale default bridge network %s (%s)", nwConfig.ID, nwConfig.BridgeName)
-				return defaultBridgeNetworkConflict{nwConfig.ID}
-			}
-
 			return types.ForbiddenErrorf("cannot create network %s (%s): conflicts with network %s (%s): %s",
 				config.ID, config.BridgeName, nwConfig.ID, nwConfig.BridgeName, err.Error())
 		}