dnsmasq: backport tweak ICMP ping logic for DHCPv4

Don't start ping-check of address in DHCP discover if there already
exists a lease for the address. It has been reported under some
circumstances android and netbooted windows devices can reply to
ICMP pings if they have a lease and thus block the allocation of
the IP address the device already has during boot.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

package/network/services/dnsmasq/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dnsmasq
 PKG_VERSION:=2.77
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=http://thekelleys.org.uk/dnsmasq/

package/network/services/dnsmasq/patches/010-Tweak-ICMP-ping-check-logic-for-DHCPv4.patch

@@ -0,0 +1,25 @@
+From 4bb68866a8aeb31db8100492bceae051e33be5d0 Mon Sep 17 00:00:00 2001
+From: Simon Kelley <simon@thekelleys.org.uk>
+Date: Thu, 15 Jun 2017 23:18:44 +0100
+Subject: [PATCH] Tweak ICMP ping check logic for DHCPv4.
+
+---
+ src/rfc2131.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/rfc2131.c b/src/rfc2131.c
+index 1c850e5..75792da 100644
+--- a/src/rfc2131.c
++++ b/src/rfc2131.c
+@@ -1040,7 +1040,7 @@ size_t dhcp_reply(struct dhcp_context *context, char *iface_name, int int_index,
+ 		  else if (have_config(config, CONFIG_DECLINED) &&
+ 			   difftime(now, config->decline_time) < (float)DECLINE_BACKOFF)
+ 		    my_syslog(MS_DHCP | LOG_WARNING, _("not using configured address %s because it was previously declined"), addrs);
+-		  else if (!do_icmp_ping(now, config->addr, 0, loopback))
++		  else if ((!lease || lease->addr.s_addr != config->addr.s_addr) && !do_icmp_ping(now, config->addr, 0, loopback))
+ 		    my_syslog(MS_DHCP | LOG_WARNING, _("not using configured address %s because it is in use by another host"), addrs);
+ 		  else
+ 		    conf = config->addr;
+-- 
+1.9.1
+