[IT4.7] Add network activity info into dumpsys for debugging

Add network activity info into part of ConnectivityService dump
for debugging.

Sample dump:

Legacy network activity:
  mNetworkActive=true
  Idle timers:
    wlan0:
      timeout=15 type=1

Bug: 170598012
Test: adb shell dumpsys connectivity
Change-Id: Ie03e82767564543d8d143873d7ddc0ea07102cb2