[PATCH] IB/mthca: assign ACK timeout field correctly

The hardware reads the ACK timeout field from the most significant 5
bits of struct mthca_qp_path's ackto field, not the least significant
bits.  This fix has the driver put the timeout in the right place.
Without this, we get a timeout that is 2^8 times too small.

Signed-off-by: Roland Dreier <rolandd@cisco.com>