wlantest: Replace pcap header directory

The use of the pcap subdirectory seems to be limited to some of the
newer Linux distros only, so use the older paths to pcap.h and
pcap-bpf.h to make wlantest bit more easier to compile on older
systems.

wlantest/readpcap.c

@@ -13,7 +13,7 @@
  */
 
 #include "utils/includes.h"
-#include <pcap/pcap.h>
+#include <pcap.h>
 
 #include "utils/common.h"
 #include "wlantest.h"

wlantest/writepcap.c

@@ -13,8 +13,8 @@
  */
 
 #include "utils/includes.h"
-#include <pcap/pcap.h>
-#include <pcap/bpf.h>
+#include <pcap.h>
+#include <pcap-bpf.h>
 
 #include "utils/common.h"
 #include "wlantest.h"