smb/client: decode reparse metadata using its payload type

cifs_open_info_data stores FILE_ALL_INFORMATION and SMB3 POSIX query
information in a union. reparse_info_to_fattr() selects a union member
from the mount mode, while several directory checks always read
fi.Attributes.

The metadata can instead come from an SMB2 CREATE response on a POSIX
mount, or from a POSIX query while processing a reparse point. In those
cases the mount mode and hard-coded fi accesses select the wrong union
member.

See the procedures below:

  cifs_nt_open
    smb2_open_file
      SMB2_open
        data->fi = SMB2 CREATE response
        data->contains_posix_file_info = false
    cifs_get_inode_info
      reparse_info_to_fattr
        if (tcon->posix_extensions) // true
          smb311_posix_info_to_fattr
            data->posix_fi // wrong union member

  smb311_posix_get_fattr
    smb2_query_path_info
      smb2_compound_op
        data->posix_fi = SMB3 POSIX query response
        data->contains_posix_file_info = true
    reparse_info_to_fattr
      data->fi.Attributes // wrong union member

Add a common DOS attribute accessor and use contains_posix_file_info
both for attribute reads and for the final fattr conversion.

Signed-off-by: Ze Tan <tanze@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>