Fix up header file names for old libpcap versions

--- ppp-2.4.3/pppd/demand.c	2004-11-04 10:02:26.000000000 +0000
+++ ppp-2.4.3/pppd/demand.c	2004-11-23 11:42:09.000000000 +0000
@@ -44,7 +44,7 @@
 #include <sys/stat.h>
 #include <sys/socket.h>
 #ifdef PPP_FILTER
-#include <pcap-bpf.h>
+#include <net/bpf.h>
 #endif
 
 #include "pppd.h"
--- ppp-2.4.3/pppd/sys-linux.c	2004-11-23 11:28:35.000000000 +0000
+++ ppp-2.4.3/pppd/sys-linux.c	2004-11-23 11:42:59.000000000 +0000
@@ -136,7 +136,7 @@
 #endif /* IPX_CHANGE */
 
 #ifdef PPP_FILTER
-#include <pcap-bpf.h>
+#include <net/bpf.h>
 #include <linux/filter.h>
 #endif /* PPP_FILTER */
 
--- ppp-2.4.3/pppd/Makefile.linux	2005-02-10 10:28:50.000000000 +0000
+++ ppp-2.4.3/pppd/Makefile.linux	2005-02-10 10:29:46.000000000 +0000
@@ -172,7 +172,7 @@
 endif
 
 ifdef FILTER
-ifneq ($(wildcard /usr/include/pcap-bpf.h),)
+ifneq ($(wildcard /usr/include/net/bpf.h),)
 LIBS    += -lpcap
 CFLAGS  += -DPPP_FILTER
 endif
--- ppp-2.4.3/pppd/Makefile.linux.lib64	2005-02-10 10:28:55.000000000 +0000
+++ ppp-2.4.3/pppd/Makefile.linux.lib64	2005-02-10 10:29:57.000000000 +0000
@@ -171,7 +171,7 @@
 endif
 
 ifdef FILTER
-ifneq ($(wildcard /usr/include/pcap-bpf.h),)
+ifneq ($(wildcard /usr/include/net/bpf.h),)
 LIBS    += -lpcap
 CFLAGS  += -DPPP_FILTER
 endif
--- ppp-2.4.3/pppd/Makefile.linux.make	2005-02-10 10:29:04.000000000 +0000
+++ ppp-2.4.3/pppd/Makefile.linux.make	2005-02-10 10:30:10.000000000 +0000
@@ -171,7 +171,7 @@
 endif
 
 ifdef FILTER
-ifneq ($(wildcard /usr/include/pcap-bpf.h),)
+ifneq ($(wildcard /usr/include/net/bpf.h),)
 LIBS    += -lpcap
 CFLAGS  += -DPPP_FILTER
 endif