RDS: TCP: Call pskb_extract() helper function

rds-stress experiments with request size 256 bytes, 8K acks,
using 16 threads show a 40% improvment when pskb_extract()
replaces the {skb_clone(..); pskb_pull(..); pskb_trim(..);}
pattern in the Rx path, so we leverage the perf gain with
this commit.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/tcp_recv.c

@@ -207,22 +207,14 @@ static int rds_tcp_data_recv(read_descriptor_t *desc, struct sk_buff *skb,
 		}
 
 		if (left && tc->t_tinc_data_rem) {
-			clone = skb_clone(skb, arg->gfp);
+			to_copy = min(tc->t_tinc_data_rem, left);
+
+			clone = pskb_extract(skb, offset, to_copy, arg->gfp);
 			if (!clone) {
 				desc->error = -ENOMEM;
 				goto out;
 			}
 
-			to_copy = min(tc->t_tinc_data_rem, left);
-			if (!pskb_pull(clone, offset) ||
-			    pskb_trim(clone, to_copy)) {
-				pr_warn("rds_tcp_data_recv: pull/trim failed "
-					"left %zu data_rem %zu skb_len %d\n",
-					left, tc->t_tinc_data_rem, skb->len);
-				kfree_skb(clone);
-				desc->error = -ENOMEM;
-				goto out;
-			}
 			skb_queue_tail(&tinc->ti_skb_list, clone);
 
 			rdsdebug("skb %p data %p len %d off %u to_copy %zu -> "