Rename net_is_disabled, net_is_completely_disabled, and PERIODIC_EVENT_FLAG_NEED_NET
The net_is_disabled() function returns true when we are in soft hibernation, which can be confusing, and which is probably a partial cause of #32108 (moved). Similarly, PERIODIC_EVENT_FLAG_NEED_NET prevents a callback from running when we are in soft hibernation, which is also potentially confusing.
Let's figure out good names for these functions and flags, and audit their usage to make sure that there are no more bugs kicking around.