Removed bad hacks in vcan.c and slcan_attach.c.

Giving some hints for users of older kernels than 2.6.25 that a 
compilation error is a normal behaviour in these cases.

Makefile

@@ -40,13 +40,15 @@
 #
 #  Send feedback to <socketcan-users@lists.berlios.de>
 
+MAKEFLAGS = -k
+
 CFLAGS    = -O2 -Wall -Wno-parentheses -I../kernel/2.6/include \
 	    -fno-strict-aliasing \
 	    -DPF_CAN=29 \
 	    -DAF_CAN=PF_CAN
 
 PROGRAMS = candump cansniffer cansend canplayer canlogserver cangen\
-	   canbusload log2long log2asc asc2log slcan_attach vcan
+	   canbusload log2long log2asc asc2log vcan slcan_attach
 
 all: $(PROGRAMS)
 

slcan_attach.c

@@ -55,7 +55,10 @@
 //#include <asm/termios.h> /* ldiscs for each arch up to 2.6.20 */
 
 #ifndef N_SLCAN
-#define N_SLCAN 17 /* bad hack until it's not inside the Kernel */
+#error Your kernel includes do not provide the needed line discipline.
+#error This is a normal behaviour for Kernel versions < v2.6.25 .
+#error You might update or patch your kernel OR you can just ignore
+#error this compilation failure if you do not need the slcan driver.
 #endif
 
 void usage(char *name)

vcan.c

@@ -28,17 +28,12 @@
 
 #include <linux/if_link.h>
 
-#if 0
-#define IFLA_LINKINFO 18
-
-enum
-{
-	IFLA_INFO_UNSPEC,
-	IFLA_INFO_NAME,
-	IFLA_INFO_DATA,
-	IFLA_INFO_XSTATS,
-	__IFLA_INFO_MAX,
-};
+#ifndef IFLA_LINKINFO
+#error Your kernel includes do not provide the needed netlink interface function.
+#error This is a normal behaviour for Kernel versions < v2.6.24 .
+#error You don't need this tool for Kernel versions < v2.6.24 anyway, as
+#error the number of vcan driver instances can be defined as a vcan.ko module
+#error commandline parameter (default = 4) in older Kernels.
 #endif
 
 #define NLMSG_TAIL(nmsg)						\