added new 'ifcfg' option to configure network

Simple examples are ifcfg=*=dhcp (configure all devices with dhcp) or
ifcfg=eth0=10.0.1.1/24,10.0.1.254 (eth0: static setup, ip 10.0.1.1,
netmask 255.255.255.0, gateway 10.0.1.254). See linuxrc docu for more.

The main difference to the existing (old) network setup strategy is that
'ifcfg' just creates config files in /etc/sysconfig/network and runs wicked.
It doesn't 'try' the config on every interface until one works.