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