Bluetoth: Host: ATT: Fix buffer allocation warnings in system workqueue

The buffer allocation in conn.c will trigger warnings if we try to use
anything else than K_NO_WAIT for the timeout when called from within the
system workqueue.

The bt_att_chan_create_pdu() already has handling for failed allocations
so this shouldn't cause any adverse effects.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>

Author: jhedberg

subsys/bluetooth/host/att.c

@@ -723,14 +723,19 @@ static struct net_buf *bt_att_chan_create_pdu(struct bt_att_chan *chan, uint8_t
 		return NULL;
 	}
 
-	switch (att_op_get_type(op)) {
-	case ATT_RESPONSE:
-	case ATT_CONFIRMATION:
-		/* Use a timeout only when responding/confirming */
-		timeout = BT_ATT_TIMEOUT;
-		break;
-	default:
-		timeout = K_FOREVER;
+	/* We can't block in the system workqueue */
+	if (k_current_get() == k_work_queue_thread_get(&k_sys_work_q)) {
+		timeout = K_NO_WAIT;
+	} else {
+		switch (att_op_get_type(op)) {
+		case ATT_RESPONSE:
+		case ATT_CONFIRMATION:
+			/* Use a timeout only when responding/confirming */
+			timeout = BT_ATT_TIMEOUT;
+			break;
+		default:
+			timeout = K_FOREVER;
+		}
 	}
 
 	/* This will reserve headspace for lower layers */