IB/mlx4: Add strong ordering to local inval and fast reg work requests

The ConnectX Programmer's Reference Manual states that the "SO" bit
must be set when posting Fast Register and Local Invalidate send work
requests.  When this bit is set, the work request will be executed
only after all previous work requests on the send queue have been
executed.  (If the bit is not set, Fast Register and Local Invalidate
WQEs may begin execution too early, which violates the defined
semantics for these operations)

This fixes the issue with NFS/RDMA reported in
<http://lists.openfabrics.org/pipermail/general/2009-April/059253.html>

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Cc: <stable@kernel.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>