(e.g: can't insert new entry into the Fragment Table, or invalid/timed-out fragment),
then the function will free all associated with the packet fragments,
mark the table entry as invalid and return NULL to the caller.
(e.g: can't insert new entry into the Fragment Table, or invalid/timed-out fragment),
then the function will free all associated with the packet fragments,
mark the table entry as invalid and return NULL to the caller.