File pdnsd-net_if_h-vs-linux_if_h.patch of Package pdnsd

Subject: fix net/if.h vs linux/if.h include order conflicts
From: Stefan Seyfried <seife+obs@b1-systems.com>

Suddenly, probably after glibc or kernel-headers update, the build fails
with this error (and following are more similar errors)

| In file included from /usr/include/linux/icmp.h:24,
|                  from icmp.c:44:
| /usr/include/net/if.h:44:5: error: redeclaration of enumerator 'IFF_UP'
|    44 |     IFF_UP = 0x1,               /* Interface is up.  */
|       |     ^~~~~~
| /usr/include/linux/if.h:83:9: note: previous definition of 'IFF_UP' with type 'enum net_device_flags'
|    83 |         IFF_UP                          = 1<<0,  /* sysfs */
|       |         ^~~~~~

this is caused by something down the include chaing including first linux/if.h
and something else including net/if.h later. net/if.h breaks if it is included
after linux/if.h. linux/if.h has provisions for net/if.h being included first.
So the fix is to include net/if.h explicitly before the others, to work around
the issue and fix the build.

Index: b/src/icmp.c
===================================================================
--- a/src/icmp.c
+++ b/src/icmp.c
@@ -39,6 +39,7 @@
 #include <string.h>
 #include "ipvers.h"
 #if (TARGET==TARGET_LINUX)
+# include <net/if.h>
 # include <netinet/ip.h>
 # include <linux/types.h>
 # include <linux/icmp.h>