contrib: bump pjsip to 2.5.5

* bump pjsip version in contrib to 2.5.5
* adapt sipvoiplink to UAS dialog API change
* add patch for Android
* rebase the gnutls patch:
 - implement new method pj_ssl_sock_start_accept2
 - add back the diff stat
 - update copyright to 2016

Major changes in pjsip 2.5.5:
* IPv6 support in PJNATH
* IPv6 support in PJLIB-UTIL DNS SRV and DNS AAAA resolution
* IPv6 support for hostname resolution in PJSIP and PJSUA-LIB

Tuleap: #62
Change-Id: I098bce4e5f36fb177de24ccb98a310673068b756