fix: #306, #394, #185, #161
break changes:
we won't create or maintain the interface now, so it is user's duty to
create the tun interface, for example, with command like
ip tuntap add dev hytun mode tun
(or maybe we can use songgao/water to keep this behavior unchanged).
correspondingly, the "address", "gateway", "mask", "dns", "persist"
options in the "tun" config have been removed.
in addition, please note xjasonlyu/tun2socks is licensed under GPLv3 and
hysteria is licensed under MIT, I don't ensure is it legal to use it as
a go mod, but there are too many requests related on it so whatever...