Revision 237059

MFC r234188,r234463,r234465:

- Update the swi_add prototype after struct ithd was split up into
  struct intr_event and struct intr_thread. [1]
- Update the rest of struct ithd references.
- net_ih and softclock_ih cookies have gone away.
- Document swi_remove(9).

PR:		docs/166864 [1]