Fixed FlexRAN-related warnings

openair2/ENB_APP/CONTROL_MODULES/MAC/flexran_agent_mac.c

...air2/ENB_APP/CONTROL_MODULES/MAC/flexran_agent_mac_defs.h

.../ENB_APP/CONTROL_MODULES/MAC/flexran_agent_mac_internal.c

openair2/ENB_APP/enb_config.c

openair2/ENB_APP/flexran_agent.c

openair2/ENB_APP/flexran_agent_common.c

openair2/ENB_APP/flexran_agent_common.h

openair2/ENB_APP/flexran_agent_common_internal.c

openair2/ENB_APP/flexran_agent_handler.c

openair2/LAYER2/MAC/eNB_scheduler_dlsch.c

openair2/LAYER2/MAC/flexran_agent_mac_proto.h

openair2/LAYER2/MAC/flexran_agent_scheduler_dataplane.c

openair2/LAYER2/MAC/flexran_agent_scheduler_dlsch_ue.c

openair2/UTIL/ASYNC_IF/link_manager.c