Allow setting sysctls on a particular interface

Signed-off-by: Piotr Skamruk <piotr.skamruk@gmail.com>

plugins/meta/tuning/tuning.go

@@ -325,6 +325,11 @@ func cmdAdd(args *skel.CmdArgs) error {
 
 	err = ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		for key, value := range tuningConf.SysCtl {
+			// If the key contains `IFNAME` - substitute it with args.IfName
+			// to allow setting sysctls on a particular interface, on which
+			// other operations (like mac/mtu setting) are performed
+			key = strings.Replace(key, "IFNAME", args.IfName, 1)
+
 			fileName := filepath.Join("/proc/sys", strings.Replace(key, ".", "/", -1))
 
 			// Refuse to modify sysctl parameters that don't belong