IB/mad: Change ib_response_mad signature arguments

ib_response_mad only needs read access to the MAD header, not write access
to the entire mad struct, so replace struct ib_mad with const struct
ib_mad_hdr

Reviewed-By: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

include/rdma/ib_mad.h

@@ -263,7 +263,7 @@ struct ib_mad_send_buf {
  * ib_response_mad - Returns if the specified MAD has been generated in
  *   response to a sent request or trap.
  */
-int ib_response_mad(struct ib_mad *mad);
+int ib_response_mad(const struct ib_mad_hdr *hdr);
 
 /**
  * ib_get_rmpp_resptime - Returns the RMPP response time.