Log only the first line of user input on PROXY protocol v1 error.

Log only the first line of user input on PROXY protocol v1 error.

Previously, all received user input was logged.  If a multi-line text was
received from client and logged, it could reduce log readability and also make
it harder to parse nginx log by scripts.  The change brings to PROXY protocol
the same behavior that exists for HTTP request line in
ngx_http_log_error_handler().