INT 2F U - DOS 3+ internal - DECREMENT SFT REFERENCE COUNT
AX = 1208h
ES:DI -> SFT
Return: AX = original value of reference count
Notes:  if the reference count was 1, it is set to FFFFh (since 0 indicates
that the SFT is not in use).  It is the caller's responsibility to
set the reference count to zero after cleaning up.
used by network redirectors such as MSCDEX

See also: 2F1106

2F1208 - DOS 3+ internal - DECREMENT SFT REFERENCE COUNT