get_basic_constraints
Description:
Get the basic constraints for the certificate if present.
 If false is returned then no basic constraints are present and the is_ca and path_len
       arguments are not changed.
Parameters:
| this | 
           the certificate  | 
      
| is_ca | 
           location to place a true if is an authority  | 
      
| path_len | 
           location to place the max path length  | 
      
Returns:
| 
           whether basic constraints are present or not  |