RRC: add an option to enable measurement reports

In the configuration file, to enable measurements, add:

    enable_measurement_reports = "yes";

Note that if x2 is enabled then the option 'enable_measurement_reports'
is not taken into account and the measurements are enabled.

openair2/COMMON/rrc_messages_types.h

@@ -180,6 +180,9 @@ typedef struct RrcConfigurationReq_s {
   uint8_t             mnc_digit_length[PLMN_LIST_MAX_SIZE];
   uint8_t             num_plmn;
 
+  int                 enable_measurement_reports;
+  int                 enable_x2;
+
   uint32_t            rrc_inactivity_timer_thres; // for testing, maybe change later
 
   paging_drx_t            default_drx;