Remove or extend UDP listening timeout

[fortuna]

If a read hits the timeout, we stop listening for packets: https://github.com/Jigsaw-Code/outline-go-tun2socks/blob/ab0408a6d301b3a55105b94255c1d436c4f6480d/shadowsocks/udp.go#L52-L56

I wonder if this is causing issues with apps that use UDP, specially in extreme conditions.

The default timeout is 30 seconds: https://github.com/Jigsaw-Code/outline-go-tun2socks/blob/2f14928f97f3730e8c5c387003284db8fc12b445/outline/tunnel.go#L84

It's not clear to me that we need the timeout. Tun2socks stack will supposedly call udpHandler.Close() when the app socket is closed.

My suggestion is to remove the timeout. At least make is longer, like the 5 minutes we use on the server: https://github.com/Jigsaw-Code/outline-ss-server/blob/8269318bb6268f9de5b289c31a59da7617520ce8/server.go#L50-L51