MINOR: connection: define error for reverse connect

Define a new error code for connection CO_ER_REVERSE. This will be used
to report an issue which happens on a connection targetted for reversal
before reverse process is completed.

include/haproxy/connection-t.h

@@ -241,6 +241,8 @@ enum {
 	CO_ER_SOCKS4_ABORT,      /* SOCKS4 Proxy handshake aborted by server */
 
 	CO_ERR_SSL_FATAL,        /* SSL fatal error during a SSL_read or SSL_write */
+
+	CO_ER_REVERSE,           /* Error during reverse connect */
 };
 
 /* error return codes for accept_conn() */

src/connection.c

@@ -725,6 +725,8 @@ const char *conn_err_code_str(struct connection *c)
 	case CO_ER_SOCKS4_ABORT:   return "SOCKS4 Proxy handshake aborted by server";
 
 	case CO_ERR_SSL_FATAL:     return "SSL fatal error";
+
+	case CO_ER_REVERSE:        return "Reverse connect failure";
 	}
 	return NULL;
 }