smb: client: fix missing mode bits for SMB symlinks

When instantiating inodes for SMB symlinks, add the mode bits from
@cifs_sb->ctx->file_mode as we already do for the other special files.

Cc: stable@vger.kernel.org
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>