daemon/cluster/executor/container: fix mixed pointer/value receiver

Got a linter warning on this one, and I don't think eventFilter() was
intentionally using a value (not pointer).

> Struct containerConfig has methods on both value and pointer receivers.
> Such usage is not recommended by the Go Documentation

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/cluster/executor/container/container.go

@@ -720,7 +720,7 @@ func (c *containerConfig) applyPrivileges(hc *enginecontainer.HostConfig) {
 	}
 }
 
-func (c containerConfig) eventFilter() filters.Args {
+func (c *containerConfig) eventFilter() filters.Args {
 	return filters.NewArgs(
 		filters.Arg("type", events.ContainerEventType),
 		filters.Arg("name", c.name()),