utils: iptables: Use go-iptables' ChainExists()

Starting with v0.5.0, go-iptables exports a fast ChainExists() which
does not rely upon listing all chains and searching the results but
probes chain existence by listing its first rule. This should make a
significant difference in rulesets with thousands of chains.

Signed-off-by: Phil Sutter <psutter@redhat.com>

plugins/meta/portmap/chain.go

@@ -103,7 +103,7 @@ func (c *chain) teardown(ipt *iptables.IPTables) error {
 
 // check the chain.
 func (c *chain) check(ipt *iptables.IPTables) error {
-	exists, err := utils.ChainExists(ipt, c.table, c.name)
+	exists, err := ipt.ChainExists(c.table, c.name)
 	if err != nil {
 		return err
 	}