The work completion length for a receiving a UD send with immediate is
short by 4 bytes causing application using this opcode to fail.

The UD receive logic incorrectly subtracts 4 bytes for immediate
value. These bytes are already included in header length and are used to
calculate header/payload split, so the result is these 4 bytes are
subtracted twice, once when the header length subtracted from the overall
length and once again in the UD opcode specific path.

Remove the extra subtraction when handling the opcode.

Fixes: 77241056 ("IB/hfi1: add driver files")
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>