OnPacket conflict between gopacket.example.go and tls.downgrade.go

Hey all,
so I did build two paket.proxy-plugins you had provided, which are gopacket.example.go and tls.downgrade.go.

tls.downgrade.go is fixed by @buffermet . Thanks, boss!

gopacket.example.go and tls.downgrad.go were built successfully.

But as I tried to build bettercap with this:
make build

I got these:
go build -o bettercap .
./tls.downgrade.go:74:6: OnPacket redeclared in this block
previous declaration at ./gopacket.example.go:11:41
make: *** [Makefile:10: build] Error 2

What did I do wrong?

Environment:
OS version and architecture you are using: Kali GNU/Linux Rolling 2019.4
Go version if building from sources: go version go1.13.4 linux/amd64