Update tsg/gopacket to HEAD as of 8c16bb8

[jasperla]

This includes two new commits:

• tsg/gopacket@23b7ce9
• tsg/gopacket@5db802b

The first one adds support for OpenBSD to gopacket, and by extension packetbeat. The latter removes an unneeded check of PFLog packets. While this code is currently unused in Packetbeat, it will allow at some point to decode pflog packets.

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[andrewkroh]

The gopacket patch file used for Windows cross-compilation is out-of-date.

Execute /scripts/before_build.sh github.com/elastic/beats
patching file vendor/github.com/tsg/gopacket/pcap/pcap.go
Hunk #1 FAILED at 8.
1 out of 1 hunk FAILED -- saving rejects to file vendor/github.com/tsg/gopacket/pcap/pcap.go.rej