network bootscript: Don't run ifup if route already set

Otherwise, warnings are issued when changing runlevel. "ip route"
is a good test of whether network is already up. If users want to
change some config, they should use ifup/down, not the network
bootscript.

bootscripts/lfs/init.d/network

@@ -29,6 +29,8 @@
 
 case "${1}" in
    start)
+      # if the default route exists, network is already configured
+      if ip route | grep -q "^default"; then return 0; fi
       # Start all network interfaces
       for file in /etc/sysconfig/ifconfig.*
       do