Use the net-utils-device-common version of HexDump

KeepaliveTracker is included in ConnectivityService mainline
module and it will not be able to access internal util class
com.android.internal.util.HexDump. Use the HexDump defined in
net-utils-device-common to remove dependency on internal util
class.

Bug: 177046265
Test: FrameworksNetTests
Change-Id: I1f5a6a749106b98e2baf22d6a290dcf8b51a6c36