bpf: add security considerations to package docs

Change-Id: I9d9bd9b66f6b5290ecd356fcefb1659d6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/net/+/795780
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>

Author: neild

bpf/doc.go

@@ -49,6 +49,13 @@ to extensions, which are essentially calls to kernel utility
 functions. Currently, the only extensions supported by this package
 are the Linux packet filter extensions.
 
+# Security Considerations
+
+The implementation of the BPF VM in this package is suitable for
+testing BPF programs. It aims for consistency with other BPF VM
+implementations, but divergence in behavior is not considered a
+security issue.
+
 # Examples
 
 This packet filter selects all ARP packets.