[AWARE] Data-path creation roles hard-coded for discovery sessions

Data-path roles (initiator & responder) are hard-coded for discovery
session participants by the spec: subscriber <-> initiator and
publisher <-> responder. Remove API parameter which allowed caller
to specify role.

(cherry-pick of commit 9c7483fec41db681a2d6de93a9061fb8764ecba5)

Bug: 32883026
Test: unit-tests and integration (sl4a) tests passing.
Change-Id: I889eacda9416d9ecd04caa0c72413f984611d40c