Various small things in the Register method

[shutterbug2000]

It seems the string() function is outputting either a pointer of some kind, or the int as raw data. Either way, it doesn't output the port as normal text.

I only noticed it by comparing packets from Nintendo's server and this one (while working on another game's server).
Whether it will cause issues? I'm not sure. Just figured I'd bring it up :p

This is the line I'm referring to:
https://github.com/PretendoNetwork/super-mario-maker-secure/blob/34b4475429545b8c3396a5eece10f0dafcbb699d/register.go#L12

[shutterbug2000]

This might cause issues too (setting the response method as RegisterEx, while responding to Register)

https://github.com/PretendoNetwork/super-mario-maker-secure/blob/34b4475429545b8c3396a5eece10f0dafcbb699d/register.go#L29

[jonbarrow]

Do you wanna open a quick PR? Or I can just change these things manually