IB/core: Add ability for drivers to report an alternate MAD size.

Add max MAD size to the device immutable data set and have all drivers that
support MADs report the current IB MAD size (IB_MGMT_MAD_SIZE) to the core.

Verify MAD size data in both the MAD core and when reading the immutable data.

OPA drivers will report alternate MAD sizes in subsequent patches.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>