In the CAPWAP spec, Data Transfer Request messages are sent by the WTP to the
AC when the WTP determines that it has important information to send to
the AC.  This is is essentially a "push" mechanism that is used to transfer 
crash files etc. to the AC, and works well for remote debugging.

However, it's desirable to have a mechanism by which the AC can "pull"
data related to crashes etc. from the WTP. This would be helpful when
debugging from the CLI.

We should make data transfer bi-directional so that both "push" and
"pull" models are supported.