Updated to latest stable, 4.0.0. USE_TOOLS+=pkg-config; Buildlink libcares
and pthread. Updated patches to reflect changes in source files. From
ChangeLog:
        * modify configuration APIs to use eXosip_set_option
        * fix bug: do not create new PRACK if it already exist for an answer.
        * update to latest osip // test time compensation for android.
        * use ephemaral port in standard TCP and TLS version.
        * return tid number so that we can match the response event.
        * use system independant time for osip_gettimeofday on unix platform.
        * major API update: several "struct eXosip_t" can be
          handled at the same time. This can be used to have several
          transport layer running at the same time.
        * many tiny other change.
check if system supports ipv6