ipv4, ipv6: avoid slice bounds panics on empty batch or BPF filter

Return 0, nil from ReadBatch and WriteBatch when ms is empty on non-Linux
platforms (matching the Linux behavior), and return an error from SetBPF
when the filter slice is empty or exceeds MaxUint16 instructions.

Change-Id: I8863524004aad5a6bc5f967f02e529866a6a6964
Reviewed-on: https://go-review.googlesource.com/c/net/+/852829
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>