[openib-general] MAD agent code comments

[Sean Hefty]

A couple of comments (so far) while tracing through the MAD agent code.

* There are a couple of places where ib_get_agent_mad() will be called 
multiple times in the same execution path.  For example agent_send calls 
it, as does agent_mad_send.  I didn't check to see if the calls would 
return the same ib_agent_port_private structure.  (Would calling the 
function ib_get_agent_port() make more sense?)

* The agent code assumes that sends are completed in the order that they 
are posted.  The MAD code does not guarantee that this is the case.  (It 
cannot do this as a result of matching requests with response, handling 
timeouts, and error handling.)

- Sean