RDMA/rxe: Restore setting tot_len in the IPv4 header

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: 230bb836ee88 ("RDMA/rxe: Fix redundant call to ip_send_check")
Link: https://lore.kernel.org/r/20210729220039.18549-3-rpearsonhpe@gmail.com
Reported-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>