libwebsockets

lws_system: dhcpclient

Generic lws_system IPv4 DHCP client

 - netif and route control via lib/plat apis
 - linux plat pieces implemented
 - Uses raw ip socket for UDP broadcast and rx
 - security-aware
 - usual stuff plus up to 4 x dns server

If it's enabled for build, it holds the system
state at DHCP until at least one registered interface
has acquired a set of IP / mask / router / DNS server

It uses PF_PACKET which is Linux-only atm.  But those
areas are isolated into plat code.

TODOs

 - lease timing and reacquire
 - plat pieces for other than Linux