iproute: don't compile with -Werror

lnstat.c:169:30: error: argument to 'sizeof' in 'memset' call is the same expression as the destination; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]
     memset(th.hdr[i], 0, sizeof(th.hdr[i]));
                                ^
  cc1: all warnings being treated as errors
  make[1]: *** [lnstat.o] Error 1

pkgs/os-specific/linux/iproute/default.nix

@@ -8,7 +8,7 @@ stdenv.mkDerivation rec {
     sha256 = "0kqy30wz2krbg4y7750hjq5218hgy2vj9pm5qzkn1bqskxs4b4ap";
   };
 
-  patches = [ ./vpnc.patch ];
+  patches = [ ./vpnc.patch ./no-werror.patch ];
 
   preConfigure =
     ''

pkgs/os-specific/linux/iproute/no-werror.patch

@@ -0,0 +1,12 @@
+diff -ubr iproute2-3.8.0-orig/Makefile iproute2-3.8.0/Makefile
+--- iproute2-3.8.0-orig/Makefile	2013-04-06 00:03:21.072827860 +0200
++++ iproute2-3.8.0/Makefile	2013-04-06 00:03:25.353837862 +0200
+@@ -30,7 +30,7 @@
+ HOSTCC = gcc
+ DEFINES += -D_GNU_SOURCE
+ CCOPTS = -O2
+-WFLAGS := -Wall -Wstrict-prototypes -Werror -Wmissing-prototypes
++WFLAGS := -Wall -Wstrict-prototypes -Wmissing-prototypes
+ WFLAGS += -Wmissing-declarations -Wold-style-definition
+ 
+ CFLAGS = $(WFLAGS) $(CCOPTS) -I../include $(DEFINES)