WII_IPC_HLE/57e_305: Store link keys

This stores the address of paired devices and associated link keys.
It is needed because some adapters forget all stored link keys when
they are reset, which breaks pairings because the Wii relies on the
Bluetooth module to remember them.

It doesn't fix adapters that can't remember any link key
at all and always return 0 for the number of stored/written link keys.
For those adapters, there is no fix.

This also improves the usability of passthrough mode for adapters that
already work, since pairings will now keep working even if the link
keys get cleared by something else (for example by the host Bluetooth
stack).

Source/Core/Core/ConfigManager.h

@@ -147,6 +147,7 @@ struct SConfig : NonCopyable
   bool m_bt_passthrough_enabled = false;
   int m_bt_passthrough_pid = -1;
   int m_bt_passthrough_vid = -1;
+  std::string m_bt_passthrough_link_keys;
 
   // Fifo Player related settings
   bool bLoopFifoReplay = true;