IB/mthca: Add support for automatic path migration (APM)

Add code to modify QP operation to handle setting alternate paths for
connected QPs.

Signed-off-by: Dotan Barak <dotanb@mellanox.co.il>
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>