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))".)

openair3/SCTP/sctp_eNB_task.c

@@ -955,6 +955,11 @@ sctp_eNB_read_from_socket(
         return;
     }
 
+    if (!(flags & MSG_EOR)) {
+      SCTP_ERROR("fatal: partial SCTP messages are not handled\n");
+      exit(1);
+    }
+
     if (flags & MSG_NOTIFICATION) {
         union sctp_notification *snp;
         snp = (union sctp_notification *)buffer;