Make variable values <replaceable> in /etc/sysconfig/ifconfig.xxx example

And little rewording of some comments.

was r11556.

chapter07/network.xml

@@ -63,17 +63,18 @@
 <!-- jhalfs relies on the values for IFACE, IP, etc. If you want to change
      them, please inform the jhalfs maintainer. -->
 <screen><userinput>cd /etc/sysconfig/
-cat &gt; ifconfig.eth0 &lt;&lt; "EOF"
-<literal>ONBOOT=yes
-IFACE=eth0
-SERVICE=ipv4-static
-IP=192.168.1.2
-GATEWAY=192.168.1.1
-PREFIX=24
-BROADCAST=192.168.1.255</literal>
+cat &gt; ifconfig.<replaceable>eth0</replaceable> &lt;&lt; "EOF"
+<literal>ONBOOT=<replaceable>yes</replaceable>
+IFACE=<replaceable>eth0</replaceable>
+SERVICE=<replaceable>ipv4-static</replaceable>
+IP=<replaceable>192.168.1.2</replaceable>
+GATEWAY=<replaceable>192.168.1.1</replaceable>
+PREFIX=<replaceable>24</replaceable>
+BROADCAST=<replaceable>192.168.1.255</replaceable></literal>
 EOF</userinput></screen>
 
-	<para>您必须修改文件中的变量，使配置与您的网络环境相匹配。</para>
+    <para>您必须修改每个文件中用斜体显示的设定值，使其与您的网络环境相匹配。
+    </para>
 
     <!--para>If the <envar>ONBOOT</envar> variable is set to <quote>yes</quote> the
     System V network script will bring up the Network Interface Card (NIC) during
@@ -89,9 +90,10 @@ EOF</userinput></screen>
 
     <!--para>The <envar>IFACE</envar> variable defines the interface name,
     for example, eth0.  It is required for all network device configuration
-    files. </para-->
+    files. The filename extension must match this value.</para-->
     <para><envar>IFACE</envar> 变量指定网络接口名，例如 eth0。
-    所有网络设备配置文件都需要它。</para>
+    所有网络设备配置文件都需要它。配置文件扩展名必须与该变量的值相同。
+    </para>
 
     <!--para>The <envar>SERVICE</envar> variable defines the method used for
     obtaining the IP address. The LFS-Bootscripts package has a modular IP