Drop USE_KERNEL_HEADERS define

This was only used for providing an option to use linux/if_packet.h
instgead of netpacket/packet.h in src/ap/iapp.c. However,
netpacket/packet.h is nowadays commonly available and hostapd already
depends on it through src/l2_packet/l2_packet_linux.c, so there is no
need to continue to provide this option for the kernel header.

Signed-off-by: Jouni Malinen <j@w1.fi>

hostapd/Makefile

@@ -27,10 +27,6 @@ CFLAGS += -I$(abspath ../src/utils)
 
 export BINDIR ?= /usr/local/bin/
 
-# Uncomment following line and set the path to your kernel tree include
-# directory if your C library does not include all header files.
-# CFLAGS += -DUSE_KERNEL_HEADERS -I/usr/src/linux/include
-
 -include .config
 
 ifndef CONFIG_NO_GITVER

src/ap/iapp.c

@@ -34,11 +34,7 @@
 #include "utils/includes.h"
 #include <net/if.h>
 #include <sys/ioctl.h>
-#ifdef USE_KERNEL_HEADERS
-#include <linux/if_packet.h>
-#else /* USE_KERNEL_HEADERS */
 #include <netpacket/packet.h>
-#endif /* USE_KERNEL_HEADERS */
 
 #include "utils/common.h"
 #include "utils/eloop.h"