cifs: add FALLOC_FL_INSERT_RANGE support

Emulated via server side copy and setsize for
SMB3 and later. In the future we could compound
this (and/or optionally use DUPLICATE_EXTENTS
if supported by the server).

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>