x2ap/sctp: increase buffer size

The 5G phone OPPO has a very big UE capability (> 2KB).

We need bigger buffers to transfer this, especially in x2 handover.

Also the sctp messages need a bigger buffer.

Note: in sctp, we didn't check for partial messages, it's now
      done. When detected, we exit. To be redone differently
      if needed. (Look for "if (!(flags & MSG_EOR))".)

openair2/COMMON/x2ap_messages_types.h

@@ -205,7 +205,7 @@ typedef struct x2ap_handover_req_s {
 
   x2ap_lastvisitedcell_info_t lastvisitedcell_info;
 
-  uint8_t rrc_buffer[1024 /* arbitrary, big enough */];
+  uint8_t rrc_buffer[8192 /* arbitrary, big enough */];
   int rrc_buffer_size;
 
   int target_assoc_id;