Combine internet network connections callback

Before the change, `onInternetDataNetworkConnected` only reports the
first time internet connection come into existence, while
`onInternetDataNetworkDisconnected` reports the last internet connection
disconnects.

For listeners to be able to track all alive internet connections, this
change report whenever an internet network is connected or disconnected.

Bug: 278162776
Test: place phone call and access data
Test: daily test b/296088621
Change-Id: Ic0f9b7d21fcb7957e7499c277307816f15bbbea0