portmap: fix checkPorts result when chain does not exist

checkPorts would return nil rather than an error if the per-container
DNAT chain didn't exist, meaning CHECK would erroneously return
success rather than failure.

chain.check() already (correctly) checks that the chain exists, so
there's no need to do it separately before calling that anyway.

plugins/meta/portmap/portmap.go

@@ -127,26 +127,12 @@ func checkPorts(config *PortMapConf, containerNet net.IPNet) error {
 	}
 
 	if ip4t != nil {
-		exists, err := utils.ChainExists(ip4t, dnatChain.table, dnatChain.name)
-		if err != nil {
-			return err
-		}
-		if !exists {
-			return err
-		}
 		if err := dnatChain.check(ip4t); err != nil {
 			return fmt.Errorf("could not check ipv4 dnat: %v", err)
 		}
 	}
 
 	if ip6t != nil {
-		exists, err := utils.ChainExists(ip6t, dnatChain.table, dnatChain.name)
-		if err != nil {
-			return err
-		}
-		if !exists {
-			return err
-		}
 		if err := dnatChain.check(ip6t); err != nil {
 			return fmt.Errorf("could not check ipv6 dnat: %v", err)
 		}