net: fix GRO skb truesize update

commit 5e10da5 ("skbuff: allow 'slow_gro' for skb carring sock
reference") introduces a serious regression at the GRO layer setting
the wrong truesize for stolen-head skbs.

Restore the correct truesize: SKB_DATA_ALIGN(...) instead of
SKB_TRUESIZE(...)

Reported-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Fixes: 5e10da5 ("skbuff: allow 'slow_gro' for skb carring sock reference")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -4369,7 +4369,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
 		/* We dont need to clear skbinfo->nr_frags here */
 
-		new_truesize = SKB_TRUESIZE(sizeof(struct sk_buff));
+		new_truesize = SKB_DATA_ALIGN(sizeof(struct sk_buff));
 		delta_truesize = skb->truesize - new_truesize;
 		skb->truesize = new_truesize;
 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;