rxe: correctly calculate iCRC for unaligned payloads

rxe: correctly calculate iCRC for unaligned payloads

If RoCE PDUs being sent or received contain pad bytes, then the iCRC
is miscalculated, resulting in PDUs being emitted by RXE with an incorrect
iCRC, as well as ingress PDUs being dropped due to erroneously detecting
a bad iCRC in the PDU.  The fix is to include the pad bytes, if any,
in iCRC computations.

Note: This bug has caused broken on-the-wire compatibility with actual
hardware RoCE devices since the soft-RoCE driver was first put into the
mainstream kernel.  Fixing it will create an incompatibility with the
original soft-RoCE devices, but is necessary to be compatible with real
hardware devices.

Fixes: c4397c211d7d ("Soft RoCE driver")
Signed-off-by: Steve Wise <larrystevenwise@gmail.com>
Link: https://lore.kernel.org/r/20191203020319.15036-2-larrystevenwise@gmail.com
Signed-off-by: Doug Ledford <dledford@redhat.com>