cifs: Add support for creating NFS-style symlinks

cifs: Add support for creating NFS-style symlinks

CIFS client is currently able to parse NFS-style symlinks, but is not able
to create them. This functionality is useful when the mounted SMB share is
used also by Windows NFS server (on Windows Server 2012 or new). It allows
interop of symlinks between SMB share mounted by Linux CIFS client and same
export from Windows NFS server mounted by some NFS client.

New symlinks would be created in NFS-style only in case the mount option
-o reparse=nfs is specified, which is not by default. So default CIFS
mounts are not affected by this change.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>