fix: let ue_ip.ko compile

MAX_MOBILES_PER_ENB cannot be used to compile ue_ip
because it is defined in platform_constants.h and this
cannot be included to compile a kernel module.

Let's use NUMBER_OF_UE_MAX as it was before instead.

openair2/NETWORK_DRIVER/UE_IP/constant.h

@@ -52,7 +52,7 @@
 
 
 
-#define UE_IP_NB_INSTANCES_MAX       MAX_MOBILES_PER_ENB
+#define UE_IP_NB_INSTANCES_MAX       NUMBER_OF_UE_MAX /*MAX_MOBILES_PER_ENB*/
 
 
 #endif