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}
diff --git a/webrtc/voice_engine/test/channel_transport/udp_transport_impl.cc b/webrtc/voice_engine/test/channel_transport/udp_transport_impl.cc
index e265c1e..c44cf9e 100644
--- a/webrtc/voice_engine/test/channel_transport/udp_transport_impl.cc
+++ b/webrtc/voice_engine/test/channel_transport/udp_transport_impl.cc
@@ -2875,6 +2875,10 @@
         {
             return false;
         }
+        if(nColons < 7 && nDubbleColons == 0)
+        {
+          return false;
+        }
         if(!(nDots == 3 || nDots == 0))
         {
             return false;