Security update for libosip2 (important)

This update for libosip2 fixes the following issues:

Changes in libosip2:

• CVE-2017-7853: In libosip2 in GNU 5.0.0, a malformed SIP message can
  lead to a heap buffer overflow in the msg_osip_body_parse() function
  defined in osipparser2/osip_message_parse.c, resulting in a remote DoS.
  (boo#1034570)
• CVE-2016-10326: In libosip2 in GNU oSIP 4.1.0, a malformed SIP message
  can lead to a heap buffer overflow in the osip_body_to_str() function
  defined in osipparser2/osip_body.c, resulting in a remote DoS.
  (boo#1034571)
• CVE-2016-10325: In libosip2 in GNU oSIP 4.1.0, a malformed SIP message
  can lead to a heap buffer overflow in the _osip_message_to_str()
  function defined in osipparser2/osip_message_to_str.c, resulting in a
  remote DoS. (boo#1034572)
• CVE-2016-10324: In libosip2 in GNU oSIP 4.1.0, a malformed SIP message
  can lead to a heap buffer overflow in the osip_clrncpy() function
  defined in osipparser2/osip_port.c. (boo#1034574)