lwip: fix tcp stable test abort issue
This MR covers following changes:
1. Modify dhcp server timer to 1 seconds
2. Enable ETHARP_TRUST_IP_MAC. Consider following scenario: we are in throughput test or traffic stability test, if this option is disabled, then every 5 minutes, the IP/MAC entry in arch cache is aged out, however, the traffic continuously send to lwip from application, because there is no IP/MAC entry in ARP cache, then the packets have to be buffered in ARP queue and a ARP request is triggered, but the ARP queue can only holds 3 packets, the later packets will be dropped, then if the traffic is big, a lot of packets will be dropped here before we get the right ARP response. For TCP, this will trigger re-transmit, it's intolerable for some application, such as real time audio, if re-transmit happen, then performance of voice will be impact. For UDP, sometimes it may also cause problem, such as DHCP, if here we failed to send the DHCP here, we has to wait the DHCP timeout etc... so this option is enabled here by default.
See merge request !681
99e461c676