Add get_p2p_session_state and error handling

[maxpowa]

I considered doing something to replace remote_ip and remote_port with more idiomatic Rust, but it risks losing information if one of the parts is zero'd out. Would rather let the library consumer make that choice.

remote_addr: if state.m_nRemoteIP != 0 && state.m_nRemotePort != 0 {
    Some(SocketAddrV4::new(
        Ipv4Addr::from(state.m_nRemoteIP.to_be_bytes()),
        state.m_nRemotePort,
    ))
} else {
    None
},