After change from udp oldheaders to headers, dhcpcd needs to get server address
from ifcaddr if laddr is v4 broadcast.

Reference: /n/sources/patch/applied/dhcpd-udpheaders
Date: Wed May 16 17:58:20 CES 2007
Signed-off-by: miller@hamnavoe.com

--- /sys/src/cmd/ip/dhcpd/dhcpd.c	Wed May 16 17:55:07 2007
+++ /sys/src/cmd/ip/dhcpd/dhcpd.c	Wed May 16 17:55:03 2007
@@ -321,6 +321,8 @@
 	rp->e = rp->buf + n;
 	rp->bp = (Bootp*)rp->buf;
 	rp->up = (Udphdr*)rp->buf;
+	if (ipcmp(rp->up->laddr, IPv4bcast) == 0)
+		ipmove(rp->up->laddr, rp->up->ifcaddr);
 	rp->max = rp->buf + Udphdrsize + MINSUPPORTED - IPUDPHDRSIZE;
 	rp->p = rp->bp->optdata;
 	v4tov6(rp->giaddr, rp->bp->giaddr);