Disable to create duplicate (with same IP Address) PCEP sessions.

Session ref. entries stored in bi-map were identifed by byte array (raw IP Address of client),
casuing that already existing session in bi-map were not look-up properly => allowing to create duplicate sessions.
Changed type of bi-map's key to wrapper of byte array.

Fixed also removing of session refs. from map on channel close. Turned bi-map to map, since inverse map is not used anymore.

pcc-mock is reusing this code - need to create session negotiator factory per pcc.

Change-Id: I85670b083b6ea832f8b9a4891c812845174f03ff
Signed-off-by: Milos Fabian <milfabia@cisco.com>
Signed-off-by: Robert Varga <rovarga@cisco.com>