mlx4: Add alias_guid mechanism

For IB ports, we paravirtualize the GUID at index 0 on slaves.  The
GUID at index 0 seen by a slave is the actual GUID occupying the GUID
table at the slave-id index.

The driver, by default, requests at startup time that subnet manager
populate its entire guid table with GUIDs. These guids are then mapped
(paravirtualized) to the slaves, and appear for each slave as its GUID
at index 0.

Until each slave has such a guid, its port status is DOWN.

The guid table is cached to support special QP paravirtualization, and
event propagation to slaves on guid change (we test to see if the guid
really changed before propagating an event to the slave).

To support this caching, add capability to __mlx4_ib_query_gid() to
obtain the network view (i.e., physical view) gid at index X, not just
the host (paravirtualized) view.

Based on a patch from Erez Shitrit <erezsh@mellanox.com>

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <roland@purestorage.com>