IB/MAD: Add agent trace points

Trace agent details when agents are [un]registered.  In addition, report
agent details on send/recv.

Reviewed-by: "Ruhl, Michael J" <michael.j.ruhl@intel.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>