all: rename module

[jwhited]

The result of:

grep --include \*.go --include \*.mod -rl golang.zx2c4.com/wireguard . | xargs sed -i '' 's/golang.zx2c4.com\/wireguard/github.com\/tailscale\/wireguard-go/g'

grep --include \*.go -rl github.com/tailscale/wireguard-go . | xargs gofmt -w

tailscale/tailscale is currently pointing at a different branch, with feature-specific naming: 4fa124729667

The intent here is to generalize the branch name. With the new branch we are also pulling in the latest upstream changes. A tailscale/tailscale PR will follow to point at this commit.