Get the l2key and grouphint from the initial provisioning configuration.

The purpose of processing CMD_UPDATE_L2INFO command in the Stopped
State is just to update the initial l2key and grouphint which are
used when starting DhcpClient (e.g. for INIT-REBOOT). We can get
both of l2key and groupHint from the initial prov configuration
parcelable instead, then be able to delete CMD_UPDATE_L2INFO from
the StoppedState.

Bug: 154441742
Test: atest FrameworksNetTests NetworkStackTests
Test: atest NetworkStackIntegrationTests
Merged-In: I760957017b18975be969a2f519ec09ee4495ebad
Change-Id: I760957017b18975be969a2f519ec09ee4495ebad