Remove inconsistent conditional includes for libc5 and glibc 2.0

Wrong conditional includes intended for support of libc5 and glibc
2.0 prevented compilation under systems with alternative libcs,
such as musl. For simplicity, remove these includes necessary for
libc5 and glibc 2.0.

ipmaddr.c

@@ -24,11 +24,7 @@
 #include <arpa/inet.h>
 #include <string.h>
 
-#if defined(__GLIBC__) && (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1))
 #include <net/if.h>
-#else
-#include <linux/if.h>
-#endif
 
 #include "config.h"
 #include "intl.h"

iptunnel.c

@@ -28,13 +28,8 @@
 #include <netinet/in.h>
 #include <netinet/ip.h>
 #include <arpa/inet.h>
-#if defined(__GLIBC__) && (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1))
 #include <net/if.h>
 #include <net/if_arp.h>
-#else
-#include <linux/if.h>
-#include <linux/if_arp.h>
-#endif
 #include <linux/types.h>
 #include <linux/if_tunnel.h>
 

mii-tool.c

@@ -46,10 +46,6 @@
 #include <net/if.h>
 #include <linux/sockios.h>
 
-#ifndef __GLIBC__
-#include <linux/if_arp.h>
-#include <linux/if_ether.h>
-#endif
 #include <linux/mii.h>
 #include <linux/sockios.h>
 #include "version.h"

slattach.c

@@ -42,18 +42,11 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
+#include <termios.h>
 #include <unistd.h>
 #include <getopt.h>
 #include <linux/if_slip.h>
 
-#if defined(__GLIBC__)
-#if __GLIBC__ == 2 && __GLIBC_MINOR__ == 0
-# include <termbits.h>
-#else
-# include <termios.h>
-#endif
-#endif
-
 #include "pathnames.h"
 #include "net-support.h"
 #include "version.h"