net: usb: sr9700: stop lying about skb->truesize

Some usb drivers set small skb->truesize and break
core networking stacks.

In this patch, I removed one of the skb->truesize override.

I also replaced one skb_clone() by an allocation of a fresh
and small skb, to get minimally sized skbs, like we did
in commit 1e2c6117 ("net: cdc_ncm: reduce skb truesize
in rx path") and 4ce62d5b ("net: usb: ax88179_178a:
stop lying about skb->truesize")

Fixes: c9b37458 ("USB2NET : SR9700 : One chip USB 1.1 USB2NET SR9700Device Driver Support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240506143939.3673865-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/usb/sr9700.c

@@ -421,19 +421,15 @@ static int sr9700_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			skb_pull(skb, 3);
 			skb->len = len;
 			skb_set_tail_pointer(skb, len);
-			skb->truesize = len + sizeof(struct sk_buff);
 			return 2;
 		}
 
-		/* skb_clone is used for address align */
-		sr_skb = skb_clone(skb, GFP_ATOMIC);
+		sr_skb = netdev_alloc_skb_ip_align(dev->net, len);
 		if (!sr_skb)
 			return 0;
 
-		sr_skb->len = len;
-		sr_skb->data = skb->data + 3;
-		skb_set_tail_pointer(sr_skb, len);
-		sr_skb->truesize = len + sizeof(struct sk_buff);
+		skb_put(sr_skb, len);
+		memcpy(sr_skb->data, skb->data + 3, len);
 		usbnet_skb_return(dev, sr_skb);
 
 		skb_pull(skb, len + SR_RX_OVERHEAD);