DHCP_FIXED_NON_UDP
#define DHCP_FIXED_LEN (DHCP_FIXED_NON_UDP + DHCP_UDP_OVERHEAD)
length = DHCP_FIXED_NON_UDP + mainbufix;
length = DHCP_FIXED_NON_UDP + mainbufix;
packet->packet_length - DHCP_FIXED_NON_UDP - 4);