bus: add process_discard method for server operation
bus: add process_discard method for server operation

A server process will generally set up a number of sd-bus managed
objects and enter a while-loop.  All further interactions are
expected to take place via the registered callbacks.

Provide an alternative 'process' method on the bus to indicate to
sd-bus that the process does not intend to handle any "escaping"
messages.  This allows sd-bus to immediately error to the client
rather than the server discarding the message and the client timing
out.

Change-Id: I3bf793e9f3d4f8d330758ebd282bbf28350bf338
Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>

openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus