eNB_scheduler_mch.c: Memory corruption

The global mbms_rab_id was defined as `uint16_t` in
eNB_scheduler_mch.c but `int` in other places.  So, code that
wrotes this global would clobber the two bytes that follow the
variable in memory.

Found by `-fsanitize=address`.

openair2/LAYER2/MAC/eNB_scheduler_mch.c

@@ -84,7 +84,7 @@ get_mbsfn_sf_alloction(module_id_t module_idP, uint8_t CC_id,
 
 static uint32_t bytes_in_buffer=0;
 static uint32_t msi_pmch_stop=0;
-uint16_t mbms_rab_id=2047;//[8] = {2047,2047,2047,2047,2047,2047,2047,2047};
+int mbms_rab_id = 2047;
 static uint32_t msi_sfs=0;