Explicitly log portal detections

Bug triagers are often confused by the log messages "validation failed
with redirect to X", thinking that this is an actual failure. As it is
expected to happen when a portal is detected, change the message to
"validation detected a portal with redirect to X".

Test: atest
Change-Id: I8655f30dbb4ada4537990d93a845994a4dfbe24b
diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index d8417c1..5ae71be 100755
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -4453,7 +4453,15 @@
                 final String logMsg = !TextUtils.isEmpty(redirectUrl)
                         ? " with redirect to " + redirectUrl
                         : "";
-                log(nai.toShortString() + " validation " + (valid ? "passed" : "failed") + logMsg);
+                final String statusMsg;
+                if (valid) {
+                    statusMsg = "passed";
+                } else if (!TextUtils.isEmpty(redirectUrl)) {
+                    statusMsg = "detected a portal";
+                } else {
+                    statusMsg = "failed";
+                }
+                log(nai.toShortString() + " validation " + statusMsg + logMsg);
             }
             if (valid != wasValidated) {
                 final FullScore oldScore = nai.getScore();