[nrf fromtree] Bluetoth: Host: 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 calls in l2cap.c and att.c which may pass non-zero timeouts already
have proper handling for failed allocations, so make sure we use K_NO_WAIT
to avoid unnecessary warnings from conn.c.

Signed-off-by: Johan Hedberg <johan.hedberg@silabs.com>
(cherry picked from commit 05b16b9)
Signed-off-by: Vinayak Kariappa Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>

Author: jhedberg

subsys/bluetooth/host/att.c

@@ -671,7 +671,11 @@ static struct net_buf *bt_att_chan_create_pdu(struct bt_att_chan *chan, uint8_t
 		timeout = BT_ATT_TIMEOUT;
 		break;
 	default:
-		timeout = K_FOREVER;
+		if (k_current_get() == k_work_queue_thread_get(&k_sys_work_q)) {
+			timeout = K_NO_WAIT;
+		} else {
+			timeout = K_FOREVER;
+		}
 	}
 
 	buf = bt_l2cap_create_pdu_timeout(NULL, 0, timeout);

subsys/bluetooth/host/l2cap.c

@@ -656,6 +656,11 @@ struct net_buf *bt_l2cap_create_pdu_timeout(struct net_buf_pool *pool,
 					    size_t reserve,
 					    k_timeout_t timeout)
 {
+	if (!K_TIMEOUT_EQ(timeout, K_NO_WAIT) &&
+	    k_current_get() == k_work_queue_thread_get(&k_sys_work_q)) {
+		timeout = K_NO_WAIT;
+	}
+
 	return bt_conn_create_pdu_timeout(pool,
 					  sizeof(struct bt_l2cap_hdr) + reserve,
 					  timeout);