Remove IpClientCallbacks dependency on DhcpResults

DhcpResults should only be used inside the NetworkStack: modules are
expected to use DhcpResultsParcelable instead.

Add a compat utility so current users of DhcpResults can do the
conversion (wifi in AOSP in particular). The utility can be removed when
changes to stop depending on DhcpResults are merged in AOSP.

Bug: 149403767
Test: built, flashed, WiFi working
Original-Change: https://android-review.googlesource.com/1277608
Merged-In: I5b85c1a541ecdf9dd3e9403b9fb1c2b5aba98dd8
Change-Id: I5b85c1a541ecdf9dd3e9403b9fb1c2b5aba98dd8