The previous llnode field is moved inside another field node.
This node field is a struct __call_single_node in Linux. Here, we
simply add an anonymous struct with the llnode field inside. That
field's new name is llist now.
struct irq_work was changed in an incompatible way. I'm thinking of adding a
#define beside the new structure so that drivers can check it to determine
how to use it, and thus have a single code base working with multiple versions
of FreeBSD. What do you think?