Remove the test for linux/if_tun.h.

It has been available for years on any decent Linux distribution.
Although linux/if_tun.h is now required to compile tinc,
you can still run it on systems which only support Ethertap.

configure.in

@@ -142,12 +142,6 @@ AC_CACHE_SAVE
 
 dnl These are defined in files in m4/
 
-case $host_os in
-  *linux*)
-    tinc_TUNTAP
-  ;;
-esac
-
 tinc_OPENSSL
 tinc_ZLIB
 tinc_LZO

m4/tuntap.m4

@@ -1,44 +0,0 @@
-dnl Check to find out whether the running kernel has support for TUN/TAP
-
-AC_DEFUN([tinc_TUNTAP],
-[
-  AC_ARG_WITH(kernel,
-    AS_HELP_STRING([--with-kernel=DIR], [give the directory with kernel sources (default: /usr/src/linux)]),
-    kerneldir="$withval",
-    kerneldir="/usr/src/linux"
-  )
-  
-  AC_CACHE_CHECK([for linux/if_tun.h], tinc_cv_linux_if_tun_h,
-  [ 
-    AC_COMPILE_IFELSE(
-      AC_LANG_PROGRAM([
-        #include "$kerneldir/include/linux/if_tun.h"
-	int a = IFF_TAP;
-      ]),
-      [if_tun_h="\"$kerneldir/include/linux/if_tun.h\""],
-      [AC_COMPILE_IFELSE(
-        AC_LANG_PROGRAM([
-	  #include <linux/if_tun.h>
-          int a = IFF_TAP;
-	]),
-        [if_tun_h="default"],
-        [if_tun_h="no"]
-      )]
-    )
-  
-    if test $if_tun_h = no; then
-      tinc_cv_linux_if_tun_h=none
-    else
-      tinc_cv_linux_if_tun_h="$if_tun_h"
-    fi
-  ])
-  
-  if test $tinc_cv_linux_if_tun_h != none; then
-    AC_DEFINE(HAVE_TUNTAP, 1, [Universal tun/tap driver present])
-    if test $tinc_cv_linux_if_tun_h != default; then
-     AC_DEFINE_UNQUOTED(LINUX_IF_TUN_H, $tinc_cv_linux_if_tun_h, [Location of if_tun.h])
-    fi
-  fi
-  AC_SUBST(LINUX_IF_TUN_H)
-  AC_SUBST(HAVE_TUNTAP)
-])

src/linux/device.c

@@ -22,16 +22,8 @@
 
 #include "system.h"
 
-#ifdef HAVE_TUNTAP
-#ifdef LINUX_IF_TUN_H
-#include LINUX_IF_TUN_H
-#else
 #include <linux/if_tun.h>
-#endif
 #define DEFAULT_DEVICE "/dev/net/tun"
-#else
-#define DEFAULT_DEVICE "/dev/tap0"
-#endif
 
 #include "conf.h"
 #include "logger.h"