Reject LE COC if cid is duplicated

This is for PTS test TP/LE/CFC/BV-20-C.

The scenario is there is already one COC between DUT and PTS.
Then PTS tries to establish one more COC with same cid which
should be rejected.

Test: PTS test TP/LE/CFC/BV-20-C done by Intel (originator
of this change).

Change-Id: I094a4058ac0e7bb9d7344e66d9feafee17bc3d53
Signed-off-by: Jaganath Kanakkassery <jaganathx.kanakkassery@intel.com>
(cherry picked from commit a0b5ff41)