We might have out-of-band code calling try_module_get() from the head
domain, or from a section covered by a hard spinlock where the root
domain must not reschedule. This requires the preemption management
calls in try_module_get() (and the converse module_put()) to be
converted to their hard variant.

REVISIT: using try_module_get() from such contexts is questionable,
client domains should be fixed.