EthernetDataTracker: Set network available on connected

This change fixes state mismatch found in the bugs below,
and makes the code look consistent with disconnect().

In startMonitoring(), reconnect() is called before mNMService.registerObserver().
Then dhcpThread.run() could finish without getting interfaceLinkStateChanged() callback.
In such a case, mNetworkInfo has connected but not-available state - which is contradictory.

Bug: 8113933, 8291000, 8291039
Change-Id: I29d74f8d09dcffb97d6c9f8198811bca046fef0c