monitor: Use getter/setter functions for cur_mon

monitor: Use getter/setter functions for cur_mon

cur_mon really needs to be coroutine-local as soon as we move monitor
command handlers to coroutines and let them yield. As a first step, just
remove all direct accesses to cur_mon so that we can implement this in
the getter function later.

Signed-off-by: Kevin Wolf <[email protected]>
Message-Id: <20201005155855[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>