conn: introduce new package that splits out the Bind and Endpoint types

The sticky socket code stays in the device package for now,
as it reaches deeply into the peer list.

This is the first step in an effort to split some code out of
the very busy device package.

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

device/peer.go

@@ -12,6 +12,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"golang.zx2c4.com/wireguard/conn"
 )
 
 const (
@@ -24,7 +26,7 @@ type Peer struct {
 	keypairs                    Keypairs
 	handshake                   Handshake
 	device                      *Device
-	endpoint                    Endpoint
+	endpoint                    conn.Endpoint
 	persistentKeepaliveInterval uint16
 
 	// These fields are accessed with atomic operations, which must be
@@ -290,7 +292,7 @@ func (peer *Peer) Stop() {
 
 var RoamingDisabled bool
 
-func (peer *Peer) SetEndpointFromPacket(endpoint Endpoint) {
+func (peer *Peer) SetEndpointFromPacket(endpoint conn.Endpoint) {
 	if RoamingDisabled {
 		return
 	}