Update docstring for parse_bridge_line() in src/or/config.c

It's pretty out-of-date.

 /** Read the contents of a Bridge line from <b>line</b>. Return 0
  * if the line is well-formed, and -1 if it isn't. If
  * <b>validate_only</b> is 0, and the line is well-formed, then add
  * the bridge described in the line to our internal bridge list.
  *
  * Bridge line format:
  * Bridge [transport] IP:PORT [id-fingerprint] [k=v] [k=v] ...
  */
 /* private */ bridge_line_t *
 parse_bridge_line(const char *line)

The return types are totally different that specified, and the function does not add a well-formed bridge line to the internal bridge list as stated.