TT#13954 don't fail kernel "clean" target when build env is not there

Change-Id: I7105582c428f7fd06c0a45774cb171fa084e265f

Makefile

@@ -8,6 +8,9 @@ all:
 	$(MAKE) -C daemon
 	$(MAKE) -C recording-daemon
 	$(MAKE) -C iptables-extension
+
+with-kernel:
+	$(MAKE)
 	$(MAKE) -C kernel-module
 
 clean:

kernel-module/Makefile

@@ -34,7 +34,7 @@ modules:
 		make -C $(KBUILD) M=$(PWD) O=$(KBUILD) modules
 
 clean:
-		make -C $(KBUILD) M=$(PWD) clean
+		make -C $(KBUILD) M=$(PWD) clean || true
 
 patch:
 		../utils/patch-kernel magic "$(PWD)" "$(KERNEL)" "$(RTPENGINE_VERSION)"