IB/mad: Support alternate Base Versions when creating MADs

In preparation to support the new OPA MAD Base version, add a base version
parameter to ib_create_send_mad and set it to IB_MGMT_BASE_VERSION for current
users.

Definition of the new base version and it's processing will occur in later
patches.

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