getinfo: CURLINFO_ACTIVESOCKET: fix bad socket value

- Set user info param to the socket returned by Curl_getconnectinfo,
regardless of if the socket is bad. Effectively this means the user info
param now will receive CURL_SOCKET_BAD instead of -1 on bad socket.

- Remove incorrect comments.

CURLINFO_ACTIVESOCKET is documented to write CURL_SOCKET_BAD to user
info param but prior to this change it wrote -1.

Bug: https://github.com/bagder/curl/pull/518
Reported-by: Marcel Raad