lwip: modify dhcp timer granularity from 60s to 1s
Current DHCP granularity is 60 seconds, it's not accurate, it can cause DHCP release/rebind/renew timer
timeout at the same time, also it may renew/rebind/release at wrong time, thus cause problem.
1. modify the discover retry backoff time from (2,4,8,16,32,60,60)s to (500m,1,2,4,8,15,15)s.
2. add DHCP_DOES_ARP_CHECK to menuconfig for users to specify if do a ARP check on the offered address.
If enable, one more second will be taken in obtaining IP address.
3. update wifi libs