IB/core: Rename struct ib_ah_attr to rdma_ah_attr

This patch simply renames struct ib_ah_attr to
rdma_ah_attr as these fields specify attributes that are
not necessarily specific to IB.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Don Hiatt <don.hiatt@intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>