Refactor the ReceiveThread with PacketReader in DhcpClient.

To implement the IP address conflict detection, we need another
ReceiveThread to listen ARP packets as well. Ideally, we should
listen both of DHCP packets and ARP packets in the same thread
with DhcpClient state machine handler.

This CL replaces the ReceiveThread with PacketReader to listen
DHCP packets. After refactoring, DHCP packets are read from the
same handler thread instead of a separate receiving thread. Then
we can also leverage the same handler thread to listen the ARP
packets simultaneously via another raw socket.

Bug: 130775067
Test: atest NetworkStackTests NetworkStackIntegrationTests

Change-Id: I23e91a6c2d99cf8053e62f2ae9d78481ece6384d