This module provides a convenient wrapper around both
CMD_[CANCEL_]_REMAIN_ON_CHANNEL APIs.
Certain protocols require going offchannel to send frames, and/or
wait for a response. The frame-xchg module somewhat does this but
has some limitations. For example you cannot just go offchannel;
an initial frame must be sent out to start the procedure. In addition
frame-xchg does not work for broadcasts since it expects an ACK.
This module is much simpler and only handles going offchannel for
a duration. During this time frames may be sent or received. After
the duration the caller will get a callback and any included error
if there was one. Any offchannel request can be cancelled prior to
the duration expriring if the offchannel work has finished early.
