For some reason Netgear have removed this line. Putting it back in shouldn't concern us:
We are not using udhcp anymore, is has been replaced by dnsmasq.
Given that this factor is pretty consistent in the busybox source code (eg. it's still there in version 1.23), it would seem wiser to keep it until proven it causes problemes.
So, closing this one.
Full path:
busybox-1.13/networking/udhcp/common.h