kmodloader: add module alias awareness

kmodloader: add module alias awareness

To achieve this, the following changes are made

 - scan module folders before scaning loaded modules
 - struct module was splited into struct module_node for the avl tree
   and struct module for storing actual info about modules

The other minor fix is that module.opts is now freed in free_modules()
when appliable

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>