socks: fix incorrect port number in SOCKS4 error message

Prior to this change it appears the SOCKS5 port parsing was erroneously
used for the SOCKS4 error message, and as a result an incorrect port
would be shown in the error message.

Bug: https://github.com/curl/curl/issues/1892


Reported-by:  <Jackarain@users.noreply.github.com>