Make the incoming port changeable

Originally reported by sziszi in Bug #479692, as question 2:

Bug or Feature?
If I setted the outgoing port to x and the incoming port automatically setted to x+1. If someone know my opened outgoing port(I don't have got any UPnP capable router(Crappy chinese junk) and I can't open UPnP port) the Someone can break into my computer, right? Make the incoming port changeable please.

First answer by Guido:
About security issue, it does no matter. Port and "port+1" are both opened, so if a cracker wants to crack you he can do it in port. The problem isn't to know a opened port, a 5 years old child can know this...
About all webserver use tcp port number 80 :)
To crack someone you need to use a vulnerability in the server program.

Second answer by Guido:
p.s. if you have not opened port on router, you have not opened port+1 too.

Third answer by Guido:
2) security: it is not a security hole. But as feature, I can introduce it in a next release