iproute2: require nls infrastructure due to libelf linking

Depending on the global nls support configuration in the buildroot, the
linked libelf.so library might depend on libintl.so.

Import the nls.mk helper to set library prefixes and flags accordingly
in this case.

Ref: https://github.com/openwrt/packages/issues/7728#issuecomment-448760140
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/network/utils/iproute2/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=iproute2
 PKG_VERSION:=4.19.0
-PKG_RELEASE:=7
+PKG_RELEASE:=8
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=@KERNEL/linux/utils/net/iproute2
@@ -23,6 +23,7 @@ PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_VERSI
 
 include $(INCLUDE_DIR)/kernel.mk
 include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/nls.mk
 
 define Package/iproute2/Default
   SECTION:=net