Fix recalled party B feature flags for a failed DTMF atxfer.

Fix recalled party B feature flags for a failed DTMF atxfer.

1) B calls A with Dial option T
2) B DTMF atxfer to C
3) B hangs up
4) C does not answer
5) B is called back
6) B answers
7) B cannot initiate transfers anymore

* Add dial features datastore to recalled party B channel that is a copy
of the original party B channel's dial features datastore.

* Extracted add_features_datastore() from add_features_datastores().

* Renamed struct ast_dial_features features_caller and features_callee
members to my_features and peer_features respectively.  These better names
eliminate the need for some explanatory comments.

* Simplified code accessing the struct ast_dial_features datastore.

(closes issue ASTERISK-19383)
Reported by: lgfsantos

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@363428 65c4cc65-6c06-0410-ace0-fbb531ad65f3