Delete old IP addresses associated with the interface when setting the

DHCP-assigned IP, broadcast, and subnet.

The nl_foreach_nlmsg() gains a seq parameter that when set to non-0 will
cause nl_foreach_nlmsg() to ignore any nlmsg that has a seq number
that does not match the caller-supplied seq argument.

ndhc/netlink.c

@@ -131,7 +131,7 @@ void handle_nl_message(struct client_state_t *cs)
         ret = nl_recv_buf(cs->nlFd, nlbuf, sizeof nlbuf);
         if (ret == -1)
             break;
-        if (nl_foreach_nlmsg(nlbuf, ret, cs->nlPortId, nl_process_msgs, cs)
+        if (nl_foreach_nlmsg(nlbuf, ret, 0, cs->nlPortId, nl_process_msgs, cs)
             == -1)
             break;
     } while (ret > 0);