Bluetooth: host: Use correct user_data size for hci_rx_pool

`struct acl_data` is used even when Host flow control is not enabled.
It is written to through the `acl(buf)` accessor in `conn.c:hci_acl()`.

Hopefully no netbufs were harmed by that :/

Signed-off-by: Jonathan Rico <[email protected]>
(cherry picked from commit 792ae68)
Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: jori-nordic

subsys/bluetooth/host/buf.c

@@ -55,7 +55,7 @@ NET_BUF_POOL_FIXED_DEFINE(evt_pool, CONFIG_BT_BUF_EVT_RX_COUNT,
 			  NULL);
 #else
 NET_BUF_POOL_FIXED_DEFINE(hci_rx_pool, BT_BUF_RX_COUNT,
-			  BT_BUF_RX_SIZE, sizeof(struct bt_buf_data),
+			  BT_BUF_RX_SIZE, sizeof(struct acl_data),
 			  NULL);
 #endif /* CONFIG_BT_HCI_ACL_FLOW_CONTROL */