- Add header: include/net/mtk_dhcpd.h
- Add implementation: net/mtk_dhcpd.c
- Add Kconfig option: CONFIG_MTK_DHCPD (depends on CONFIG_HTTPD)
- Include mtk_dhcpd.o in net/Makefile
- failsafe/failsafe.c:
- call mtk_dhcpd_start() before Web failsafe starts
- call mtk_dhcpd_stop() after Web failsafe exits
- net/net.c: call mtk_dhcpd_start() after net_loop(TCP) initialization
to provide a fallback hook
