Move Ethernet related files to f/b/packages/ConnectivityT.

ethernet-service is going to be moved into Connectivity mainline module.
Move all ethernet related files in f/b/ to f/b/packages/ConnectivityT so
that it's easier to migrate these files to Connectivity module finally
after clearing the hidden API usages. Below files to be moved:

Ethernet framework related files:
    - EthernetManager.java
    - EthernetNetworkSpecifier.java
    - IEthernetManager.aidl
    - IEthernetServiceListener.aidl
    - ITetheredInterfaceCallback.aidl

Ethernet service related files:
    - IpConfigStore.java(EthernetConfigStore has dependency on the class)

For the ethernet-service related files, keep it as-is temproraliy and
fix the hiden API dependencies in f/opt/net/ethernet/. After this work
is done, then migrating the whole of ethernet folder to Connectivity
module completely.

This CL also fixes some minor errors of code style format to pass the
code style check.

Bug: 210586283
Test: build pass
      atest FrameworksNetTests
      atest EthernetServiceTests
Change-Id: Ib359d29d5221105f648bc4194c6d6dbe4cc6e3e5