global: use netip where possible now

There are more places where we'll need to add it later, when Go 1.18
comes out with support for it in the "net" package. Also, allowedips
still uses slices internally, which might be suboptimal.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tun/netstack/examples/http_client.go

@@ -1,4 +1,5 @@
 //go:build ignore
+// +build ignore
 
 /* SPDX-License-Identifier: MIT
  *
@@ -10,9 +11,9 @@ package main
 import (
 	"io"
 	"log"
-	"net"
 	"net/http"
 
+	"golang.zx2c4.com/go118/netip"
 	"golang.zx2c4.com/wireguard/conn"
 	"golang.zx2c4.com/wireguard/device"
 	"golang.zx2c4.com/wireguard/tun/netstack"
@@ -20,8 +21,8 @@ import (
 
 func main() {
 	tun, tnet, err := netstack.CreateNetTUN(
-		[]net.IP{net.ParseIP("192.168.4.29")},
-		[]net.IP{net.ParseIP("8.8.8.8")},
+		[]netip.Addr{netip.MustParseAddr("192.168.4.29")},
+		[]netip.Addr{netip.MustParseAddr("8.8.8.8")},
 		1420)
 	if err != nil {
 		log.Panic(err)