RDMA/rxe: Correct skb on loopback path

rxe_net.c sends packets at the IP layer with skb->data pointing at the IP
header but receives packets from a UDP tunnel with skb->data pointing at
the UDP header.  On the loopback path this was not correctly accounted
for.  This patch corrects for this by using sbk_pull() to strip the IP
header from the skb on received packets.

Fixes: 8700e3e ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20210128182301.16859-1-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_net.c

@@ -408,6 +408,11 @@ int rxe_send(struct rxe_pkt_info *pkt, struct sk_buff *skb)
 
 void rxe_loopback(struct sk_buff *skb)
 {
+	if (skb->protocol == htons(ETH_P_IP))
+		skb_pull(skb, sizeof(struct iphdr));
+	else
+		skb_pull(skb, sizeof(struct ipv6hdr));
+
 	rxe_rcv(skb);
 }