idpf: fix memory leak of flow steer list on rmmod

In the Linux kernel, the following vulnerability has been resolved:

idpf: fix memory leak of flow steer list on rmmod

The flow steering list maintains entries that are added and removed as ethtool creates and deletes flow steering rules. Module removal with active entries causes memory leak as the list is not properly cleaned up.

Prevent this by iterating through the remaining entries in the list and freeing the associated memory during module removal. Add a spinlock (flow_steer_list_lock) to protect the list access from multiple threads.