Display implementation for IpAddr doesn't respect width or alignment

[jethrogb]

fn main() {
    println!("{:?}", format!("{:<15}", std::net::Ipv4Addr::UNSPECIFIED));
    println!("{:?}", format!("{:>15}", std::net::Ipv4Addr::UNSPECIFIED));
}

produces

"0.0.0.0"
"0.0.0.0"

but I'd expect

"0.0.0.0        "
"        0.0.0.0"

[Goirad]

This can be closed now, at least for nightly.