DHCP_DOES_ARP_CHECK macro

LWIP_DHCP_CHECKS_OFFERED_ADDRESS: - Using Address Conflict Detection (ACD) module assures that the offered IP address is properly probed and announced before binding in DHCP. This conforms to RFC5227, but takes several seconds. - Using ARP check, we only send two ARP requests to check for replies. This process lasts 1 - 2 seconds. - No conflict detection: We directly bind the offered address.