UdpTransport:IsIpAddressValid: Added extra :: check for ipv6

The code previously allowed ipv6 addresses with less than eight sections even without all-zero sections being compacted by a ::.

BUG=webrtc:1028

Review-Url: https://codereview.webrtc.org/2606383003
Cr-Commit-Position: refs/heads/master@{#16108}

webrtc/voice_engine/test/channel_transport/udp_transport_impl.cc

@@ -2875,6 +2875,10 @@ bool UdpTransport::IsIpAddressValid(const char* ipadr, const bool ipV6)
         {
             return false;
         }
+        if(nColons < 7 && nDubbleColons == 0)
+        {
+          return false;
+        }
         if(!(nDots == 3 || nDots == 0))
         {
             return false;