rootfs: add IP configuration of management port to Kconfig

--Update /etc/init.d/network script.
Keeping lo up prevents monit from restarting dropbear and lighttpd,
then finally rebooting system due to exceeded number of maximum application's
restarts.
--keep lo ocnfiguration in /etc/network/interfaces due to above
--Update user manual

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>