Android DHCP Port Redirection
I solved this problem using DNAT redirection instead of port redirection, due to some limitations of REDIRECT involving broadcast traffic.

iptables -I INPUT -p udp --dport 67 -j ACCEPT
iptables -I INPUT -p udp --dport 6700 -j ACCEPT
iptables -I PREROUTING -t nat -i ncm0 -p udp -src 0.0.0.0 --dport 67 -j DNAT --to 0.0.0.0:6700