Rewrite `std::net::ToSocketAddrs` doc examples.
Rewrite `std::net::ToSocketAddrs` doc examples.

in particular:

* show how to create an iterator that yields multiple socket addresses
* show more failing scenarios

GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust