iproute2: fix rebuild failures

When rebuilding iproute2, many such instances of the following build failure occur:

	| make[1]: Entering directory '.../iproute2/4.14.1-r0/iproute2-4.14.1/lib'
	| Makefile:1: ../config.mk: No such file or directory
	| make[1]: *** No rule to make target '../config.mk'.  Stop.

---
 meta/recipes-connectivity/iproute2/iproute2.inc | 2 ++
 1 file changed, 2 insertions(+)

index b404eedbfb..4fbfec6f08 100644
@@ -13,6 +13,8 @@ DEPENDS = "flex-native bison-native iptables elfutils"
 
 inherit update-alternatives bash-completion pkgconfig
 
+CLEANBROKEN = "1"
+
 PACKAGECONFIG ??= "tipc"
 PACKAGECONFIG[tipc] = ",,libmnl,"
 

2.14.1.459.g238e487ea