Set initial timeout upon UDP proxy connection creation

This PR is an attempt to prevent [connections leaking forever](https://github.com/GoogleCloudPlatform/kubernetes/issues/1274). `ProxyLoop` and `proxyClient` both have `SetDeadline` calls just after they `Write` and `Read`, respectively. These deadlines set timeouts after the successful read and write. However, a leak may occur just after the connection is created as the write and/or read block the first time they are called.