fs/ntfs3: Rework ntfs_utf16_to_nls

Now ntfs_utf16_to_nls takes length as one of arguments.
If length of symlink > 255, then we tried to convert
length of symlink +- some random number.
Now 255 symbols limit was removed.

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>