veyron/runtimes/google/ipc: take care to use an IP host address and never an IP network address.

Change-Id: I9fec54c9647fc890cf6d0993e613c80940638873
diff --git a/runtimes/google/ipc/server.go b/runtimes/google/ipc/server.go
index 20047c5..a737391 100644
--- a/runtimes/google/ipc/server.go
+++ b/runtimes/google/ipc/server.go
@@ -173,7 +173,12 @@
 			addrs, err := netstate.GetAccessibleIPs()
 			if err == nil {
 				if a, err := s.preferredAddress(protocol, addrs); err == nil {
-					iep.Address = net.JoinHostPort(a.String(), port)
+					if ip := netstate.AsIP(a); ip != nil {
+						// a may be an IPNet or an IPAddr under the covers,
+						// but we really want the IP portion without any
+						// netmask so we use AsIP to ensure that.
+						iep.Address = net.JoinHostPort(ip.String(), port)
+					}
 				}
 			}
 		}