ConnectivityService: log wakelock activity in dumps

This patch adds wakelock acquire and release activity to
ConnectivityService logs in dumpsys. All of the last 20 acquire and
release operations are logged.

This patch also:
  - does a bit of cleanup to related dumpsys logs
  - unify pretty printing of internal event ids to their names.
  - delete mInetLog which was obsolete and not used.

Example of logs:
  NetTransition WakeLock activity (most recent first):
    03-30 02:15:40.628 - RELEASE 1 by EVENT_EXPIRE_NET_TRANSITION_WAKELOCK: not released (serial number was 2)
    03-30 02:15:09.965 - ACQUIRE 2 for NetworkAgentInfo [WIFI () - 101]
    03-30 02:15:01.877 - RELEASE 1 by EVENT_CLEAR_NET_TRANSITION_WAKELOCK: released
    03-30 02:14:40.598 - ACQUIRE 1 for NetworkAgentInfo [WIFI () - 100]

Test: inspected result of $ adb shell dumpsys connectivity
Bug: 36703718
Change-Id: Ia8e2016fc512ee798ef0adc3f612d1f6c33d4870