fd_msg_add_result: add function Add fd_msg_add_result() as a superset of fd_msg_rescode_set() to allow setting of either Result-Code or Experimental-Result (Grouped), depending upon whether the supplied vendor is 0 or not. Reimplement fd_msg_rescode_set() in terms of fd_msg_add_result().

This content was contributed by Krishnan Srinivasan from Allot Communication.

The dictionary entries may need some adjustments to 
match the content of the dict_dcca_3gpp extension.

Thank you Krishnan!