IP connectivity metrics: ConnectStats additions

This patch:
  - adds a counter to ConnectStats for counting the number of successful
    connect() calls done in blocking mode. This allows to compute error
    rates for connect() in blocking mode.
  - add printing of ConnectStats when dumping NetdEventListenerService
    and/or IpConnectivityMetrics service.

Test: $ runtest frameworks-net, + manual tests verifying logged events.
Bug: 34901696
Change-Id: I889e8ccd12681b0511be487e9d2ee44290a2d7d7
diff --git a/tests/net/java/com/android/server/connectivity/NetdEventListenerServiceTest.java b/tests/net/java/com/android/server/connectivity/NetdEventListenerServiceTest.java
index 637eaa3..9e0f321 100644
--- a/tests/net/java/com/android/server/connectivity/NetdEventListenerServiceTest.java
+++ b/tests/net/java/com/android/server/connectivity/NetdEventListenerServiceTest.java
@@ -219,7 +219,7 @@
                 "time_ms: 0",
                 "transports: 0",
                 "connect_statistics <",
-                "  connect_blocking_count: 0",
+                "  connect_blocking_count: 7",
                 "  connect_count: 12",
                 "  errnos_counters <",
                 "    key: 1",