net/udprelay: apply netns Control func to server socket(s)

To prevent peer relay servers from sending packets *over* Tailscale.

Updates tailscale/corp#35651

Signed-off-by: Jordan Whited <jordan@tailscale.com>

net/udprelay/server_notlinux.go

@@ -10,9 +10,7 @@ import (
 	"syscall"
 )
 
-func listenControl(_ string, _ string, _ syscall.RawConn) error {
-	return nil
-}
+func trySetReusePort(_ string, _ string, _ syscall.RawConn) {}
 
 func isReusableSocket(*net.UDPConn) bool {
 	return false