Expects: AX    0003H
ES:DI address of calling switcher's service function handler
Returns: CF    Carry Flag is clear (NC) is successful
CF is set (CY) if the switcher does not support this fn.
Info: This service is used ONLY by a task-switching program that has
previously suspended another task switcher.

Applications should not use this service.  If you need to keep a
switcher from suspending a session, you should hook into the
notification chain (via SwNtfyFn 0004H) and handle SwNtfyFn 0001H
(query suspend) calls.

INT 2fH 4bxxH (switcher functions)
- -

SwSrvc Fn 0003H: Resume Switcher