Leaf UDP support

[mukswilly]

Has anyone been able to get leaf to relay UDP traffic? If I'm not mistaken, leaf should be able to relay UDP traffic to a socks proxy server if a socks outbound is specified and as long as it supports UDP associate. According to my tests, after leaf sends the UDP associate command and the socks proxy sends back a succeeded reply with the associated address, no UDP traffic is relayed by leaf to the specified address. I had to double-check my socks proxy implementation and it is indeed not at fault as it works well with other tun2socks implementations such as the previous go-tun2socks implementation by @eycorsican That said, I would still want to use leaf as it is the only tun2socks implementation I could find that works well as regards the iOS hard limit on memory.