Add network manager, DNS configuration and ethtool

- network manager package automatically discovers ethernet
  and configures the link using DHCP
- /etc/resolv.conf populated with DNS servers enables
  name resolving service.
- ethtool is added to print debug data for ethernet
  does network bringup.
- moved priority of init.sh to 99, so that other
  startup scripts are run before it

Signed-off-by: Amrathesh <amrathesh@arm.com>