net/inet_lro: remove setting skb->ip_summed when not LRO-able

When an SKB cannot be chained to a session, the current code attempts
to "restore" its ip_summed field from lro_mgr->ip_summed. However,
lro_mgr->ip_summed does not hold the original value; in fact, we'd
better not touch skb->ip_summed since it is not modified by the code
in the path leading to a failure to chain it.  Also use a cleaer
comment to the describe the ip_summed field of struct net_lro_mgr.

Issue raised by Or Gerlitz <ogerlitz@voltaire.com>

Signed-off-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/inet_lro.h b/include/linux/inet_lro.h
index 80335b7..c4335fa 100644
--- a/include/linux/inet_lro.h
+++ b/include/linux/inet_lro.h
@@ -84,7 +84,11 @@
 				    from received packets and eth protocol
 				    is still ETH_P_8021Q */
 
-	u32 ip_summed;      /* Set in non generated SKBs in page mode */
+	/*
+	 * Set for generated SKBs that are not added to
+	 * the frag list in fragmented mode
+	 */
+	u32 ip_summed;
 	u32 ip_summed_aggr; /* Set in aggregated SKBs: CHECKSUM_UNNECESSARY
 			     * or CHECKSUM_NONE */