INT 2F U - NETWORK REDIRECTOR (DOS 3.x only) - LOCK REGION OF FILE
        AX = 110Ah
        BX = file handle
        CX:DX = starting offset
        SI = high word of size
        STACK: WORD low word of size
        ES:DI -> SFT
            SFT DPB field -> DPB of drive containing file
        SS = DOS DS
Return: CF set on error
           AL = DOS error code (see INT 21/AH=59h)
        STACK unchanged
Notes:  called by DOS 3.10-3.31 kernel
        the redirector is expected to resolve lock conflicts
SeeAlso: INT 21/AH=5Ch