RDMA/rxe: Restore setting tot_len in the IPv4 header

An earlier patch removed setting of tot_len in IPv4 headers because it was
also set in ip_local_out. However, this change resulted in an incorrect
ICRC being computed because the tot_len field is not masked out. This
patch restores that line. This fixes the bug reported by Zhu Yanjun.  This
bug affects anyone using rxe which is currently broken.

Fixes: 230bb836 ("RDMA/rxe: Fix redundant call to ip_send_check")
Link: https://lore.kernel.org/r/20210729220039.18549-3-rpearsonhpe@gmail.comReported-by: Zhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Reviewed-and-tested-by: Zhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/sw/rxe/rxe_net.c

@@ -259,6 +259,7 @@ static void prepare_ipv4_hdr(struct dst_entry *dst, struct sk_buff *skb,
 
 	iph->version	=	IPVERSION;
 	iph->ihl	=	sizeof(struct iphdr) >> 2;
+	iph->tot_len	=	htons(skb->len);
 	iph->frag_off	=	df;
 	iph->protocol	=	proto;
 	iph->tos	=	tos;