Expect: AX    0002H
BX    ID of the session that is about to be suspended
ES:DI addr of switcher's service-entry address
Return: AX    0000H if OK to suspend, as far as you're concerned
0001H if you object to the switch
Info: Task switchers first call SwNtfyFn 0001H to see if a session
switch is OK, then they call this fn directly before suspending
your session.  This is the last chance for your application to
prevent the switch.  When called, interrupts are disabled you
should NOT use any DOS fns.

BX will contain the session ID of the session that is about to be
switched out.  Global TSRs may wish to take special actions for
each session.

ES:SI will contain the task switcher's service entry address.  Use this
address if you need to call service fns such as SwSrvcFn 0001H
(test memory region) to determine how you feel about being
switched out.

Return: AX=0000H if you have no objection to being switched out. If any
task returns a non-zero value, the session will not be switched
out and all tasks may receive SwNtfyFn 0004H (session is active).

INT 2fH 4bxxH (switcher functions)
- -

SwNtfy Fn 0002H: Switcher Is Suspending Your Session