Supply a stub bpf_validate() (always returning false - the script is not

valid) if BPF is missing.
The netgraph_bpf node forced bpf to be present, reflect that in the
options.
Stop doing a 'count bpf' - we provide stubs.
Since a handful of drivers still refer to "bpf.h", provide a more accurate
indication that the API is present always. (eg: netinet6)

sys/conf/files

@@ -779,7 +779,10 @@ msdosfs/msdosfs_lookup.c	optional msdosfs
 msdosfs/msdosfs_vfsops.c	optional msdosfs
 msdosfs/msdosfs_vnops.c		optional msdosfs
 net/bpf.c		standard
-net/bpf_filter.c	count bpf
+net/bpf_filter.c	optional bpf
+bpf.h			standard			\
+	compile-with	"echo '#define NBPF 1' > bpf.h" \
+	no-obj no-implicit-rule before-depend
 net/bridge.c		optional bridge
 net/bsd_comp.c		optional ppp_bsdcomp
 #net/hostcache.c		standard

sys/conf/options

@@ -493,3 +493,4 @@ NDEVFSOVERFLOW		opt_devfs.h
 # various 'device presence' options.
 DEV_SNP			opt_snp.h
 DEV_MCA			opt_mca.h
+DEV_BPF			opt_bpf.h

sys/net/bpf.c

@@ -40,7 +40,8 @@
  * $FreeBSD$
  */
 
-#include "bpf.h"
+#include "opt_bpf.h"
+#include "opt_netgraph.h"
 
 #ifndef __GNUC__
 #define inline
@@ -80,7 +81,7 @@
 
 static MALLOC_DEFINE(M_BPF, "BPF", "BPF data");
 
-#if NBPF > 0
+#if defined(DEV_BPF) || defined(NETGRAPH_BPF)
 
 /*
  * Older BSDs don't have kernel malloc.
@@ -1396,7 +1397,7 @@ bpf_drvinit(unused)
 
 SYSINIT(bpfdev,SI_SUB_DRIVERS,SI_ORDER_MIDDLE+CDEV_MAJOR,bpf_drvinit,NULL)
 
-#else /* !BPF */
+#else /* !DEV_BPF && !NETGRAPH_BPF */
 /*
  * NOP stubs to allow bpf-using drivers to load and function.
  *
@@ -1442,4 +1443,12 @@ bpf_filter(pc, p, wirelen, buflen)
 	return -1;	/* "no filter" behaviour */
 }
 
-#endif /* !BPF */
+int
+bpf_validate(f, len)
+	const struct bpf_insn *f;
+	int len;
+{
+	return 0;		/* false */
+}
+
+#endif /* !DEV_BPF && !NETGRAPH_BPF */