net: gro: avoid re-computing truesize twice on recycle

After commit 5e10da53 ("skbuff: allow 'slow_gro' for skb
carring sock reference") and commit af352460 ("net: fix GRO
skb truesize update") the truesize of the skb with stolen head is
properly updated by the GRO engine, we don't need anymore resetting
it at recycle time.

v1 -> v2:
 - clarify the commit message (Alexander)
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/gro.c

@@ -634,7 +634,6 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 
 	skb->encapsulation = 0;
 	skb_shinfo(skb)->gso_type = 0;
-	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
 	if (unlikely(skb->slow_gro)) {
 		skb_orphan(skb);
 		skb_ext_reset(skb);