This patch follows the bump of PJSIP to 2.5.5 version, introducing IPv6
support to PJNATH library.

- ICE configuration is modified to support IPv6 STUN and TURN servers
- we add by default the host addresses in IPv6 and IPv4
  (in this order, so IPv6 can be selected in priority)

Tuleap: #891
Change-Id: Ia0355c2691e3d03346e85295265dd9acc424d58e