tests: bsim: Bluetooth: Fail throughput test with increased Tx count

Make the throughput test to fail when increasing Tx buffers
that will delay a LE Connection Ind PDU from being
transmitted on air due to previously queued Data PDUs.

Unlike legacy Zephyr Controller's double headed Tx queue
linked list, the new split Zephyr Controller's new LLCP does
not place a control PDU at the head of the queue causing
control PDUs to be delayed on air.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

Author: cvinayak

tests/bsim/bluetooth/ll/throughput/prj.conf

@@ -24,15 +24,15 @@ CONFIG_BT_BUF_CMD_TX_SIZE=255
 
 # BT HCI Event Buffers
 # Greater than BT_BUF_ACL_TX_COUNT, to be able to receive Number of Completed Packets events
-CONFIG_BT_BUF_EVT_RX_COUNT=4
+CONFIG_BT_BUF_EVT_RX_COUNT=7
 CONFIG_BT_BUF_EVT_RX_SIZE=255
 
 # BT HCI Discardable Event Buffers
 CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT=3
 CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=255
 
 # BT HCI ACL TX Data Buffers
-CONFIG_BT_BUF_ACL_TX_COUNT=3
+CONFIG_BT_BUF_ACL_TX_COUNT=6
 CONFIG_BT_BUF_ACL_TX_SIZE=251
 
 # BT HCI ACL RX Data Buffers