NFD

Currently, tables.cs_policy key of nfd.conf sets the cache replacement policy, but its change is ignored upon runtime configuration reload.
This issue is to allow changing cache replacement policy via configuration reload.

• In cs::Policy base class, add:

  public:
    void adopt();
  private:
    virtual void doAdopt();
  

  The base class doAdopt function erases all CS entries.

• When tables.cs_policy is changed during a configuration reload:

  1. Destruct the old cs::Policy subclass instance.
  2. Construct the new cs::Policy subclass instance, and invoke its adopt function.

• A policy may override the doAdopt function, where it may enumerate existing CS entries and insert them to the policy's cleanup queues.

This issue only involves configuration reload, Cs, and cs::Policy base class implementation.
It does not involve cs::Policy subclass changes or management changes