ConnectivityService: dumpsys args for dumping networks or requests only.

This patch adds two arguments to ConnectivityService dumpsys handler so
that only current networks or only current requests are dumped:

- "adb shell dumpsys connectivity networks" will dump current networks.
- "adb shell dumpsys connectivity requests" will dump current requests.

Bug: none
Test: Compiled, flashed, booted, checked that both new dumpsys args work
      as expected.

Change-Id: Ie28e6c800795eb49f386b609e8222a25e73dfc84