Add an LMC cache to struct ib_device, and add a function
ib_get_cached_lmc() to query the cache.
Signed-off-by: NJack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: NSean Hefty <sean.hefty@intel.com>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>