libpcap: fixed installation of pcap-int.h when using no prefix

network/libpcap/libpcap.conf

@@ -27,7 +27,7 @@ fi
 # enable IPv6 support by default
 var_append confopt ' ' '--enable-ipv6'
 
-hook_add postmake 5 "cp -fv pcap-int.h $root/$prefix/include/"
+hook_add postmake 5 "cp -fv pcap-int.h $root$includedir"
 
 # we need to perform some config hacking for cross compilation ... :-(
 if ! atstage native; then