Expose function for checking MYSQL connection errors

If a query done via the connector fails, the return value can be inspected
with the function. This helps separate fatal problems from transient ones.

include/maxscale/mysql_utils.h

@@ -41,6 +41,13 @@ char* mxs_lestr_consume(uint8_t** c, size_t *size);
  */
 MYSQL* mxs_mysql_real_connect(MYSQL *mysql, SERVER *server, const char *user, const char *passwd);
 
+/**
+ * Check if the MYSQL error number is a connection error
+ *
+ * @return True if the MYSQL error number is a connection error
+ */
+bool mxs_mysql_is_net_error(int errcode);
+
 /**
  * Execute a query
  *