hs20: fix linking with full language support enabled

After d18692c, we need to include nls.mk to setup correct
environment variables so that linking succeeds.

Reported-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Signed-off-by: Michael Heimpold <mhei@heimpold.de>

net/hs20/Makefile

@@ -40,6 +40,7 @@ ifdef CONFIG_USE_GLIBC
 endif
 
 include $(INCLUDE_DIR)/package.mk
+include $(INCLUDE_DIR)/nls.mk
 
 define Package/hs20-common
   SECTION:=net