Int 2F Fn 1080  U - DOS 4 Only Share Internal - Turn On File Sharing Chec  [f]

   AX = 1080h

Return: AL = status
       F0h successful
       FFh checking was already on

Note:  DOS 4.x SHARE has dual functions: FCB support for large (>32M) media
     and file sharing checks.  The undocumented commandline flag /NC can
     be used to disable the sharing code.

See Also: AX=1000h,AX=1081h