added configuration file for lowband of SoDeRa

make changes to use the fronthaul configuration parameters - updates to rrh_gw.c and eNB_transport.c wrt to changes in openair0_device struct

Work with virtual interfaces, you will have to set the eNB virtual interfaces up yourself (ifconfig ethx:y ipv4@ up)

handling of timing advance is improved. MAC retrieves timing advance from phy once prior to DL scheduling and clears the statistic in PHY. A timer for controlling the timing advance periodicity was introduced.