net/tsdial: move macOS/iOS peerapi sockopt logic from LocalBackend

Change-Id: I812cae027c40c70cdc701427b1a1850cd9bcd60c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/peerapi_macios_ext.go

@@ -9,10 +9,8 @@
 package ipnlocal
 
 import (
-	"errors"
 	"fmt"
 	"net"
-	"syscall"
 
 	"inet.af/netaddr"
 	"tailscale.com/net/interfaces"
@@ -21,7 +19,6 @@ import (
 
 func init() {
 	initListenConfig = initListenConfigNetworkExtension
-	peerDialControlFunc = peerDialControlFuncNetworkExtension
 }
 
 // initListenConfigNetworkExtension configures nc for listening on IP
@@ -34,24 +31,3 @@ func initListenConfigNetworkExtension(nc *net.ListenConfig, ip netaddr.IP, st *i
 	}
 	return netns.SetListenConfigInterfaceIndex(nc, tunIf.Index)
 }
-
-func peerDialControlFuncNetworkExtension(b *LocalBackend) func(network, address string, c syscall.RawConn) error {
-	b.mu.Lock()
-	defer b.mu.Unlock()
-	st := b.prevIfState
-	pas := b.peerAPIServer
-	index := -1
-	if st != nil && pas != nil && pas.tunName != "" {
-		if tunIf, ok := st.Interface[pas.tunName]; ok {
-			index = tunIf.Index
-		}
-	}
-	var lc net.ListenConfig
-	netns.SetListenConfigInterfaceIndex(&lc, index)
-	return func(network, address string, c syscall.RawConn) error {
-		if index == -1 {
-			return errors.New("failed to find TUN interface to bind to")
-		}
-		return lc.Control(network, address, c)
-	}
-}