add LimitNOFILE to service files

[CiXY]

在trojan-go的systemd模版中添加LimitNOFILE解决使用一段时间发生断连的情况
参考：
p4gefau1t/trojan-go#313

[malikshi]

Some vps not support that kind of setting i think.
Isn't better to set certain limit number.
LimitNOFILE=51200

[CiXY]

I have changed it on my vps. But disconnection still happened. it may need more test

[malikshi]

@CiXY you may try this

LimitNOFILE=51200
LimitNPROC=infinity

For public servers add more zero xD 512000. I set this one with traffic vnstat in vps 150-400Mbps.