rotctl: add autopark functionality

Since gpredict doesn't have a park button or anything, this will just
automatically park the antenna when the gpredict rotator controller
disconnects. This may or may not actually be a good idea. We will see.

src/Config.zig

@@ -92,6 +92,7 @@ pub fn validate(self: Config, err_writer: anytype) !void {
 rotctl: RotControlConfig = .{
     .listen_address = "127.0.0.1",
     .listen_port = 4533,
+    .autopark = true,
 },
 labjack: LabjackConfig = .{
     .device = .autodetect,
@@ -151,6 +152,7 @@ pub const MinMax = struct {
 const RotControlConfig = struct {
     listen_address: []const u8,
     listen_port: u16,
+    autopark: bool,
 };
 
 const LabjackConfig = struct {

src/RotCtl.zig

@@ -60,6 +60,11 @@ pub fn run(allocator: std.mem.Allocator) !void {
                 std.mem.trim(u8, fbs.getWritten(), &std.ascii.whitespace),
             ) catch break;
         }
+
+        // loop ended due to client disconnect
+        if (interface.running and config.rotctl.autopark) {
+            interface.rotator.startPark();
+        }
     }
 }