dhd: add missing interface command fini

From: Tanguy Pruvot <tanguy.pruvot@gmail.com>

seen on Netd init (before CM banner), and also close init socket.

W/InterfaceController:
Error (Symbol not found) while searching for the interface command fini function

Change-Id: Ib9f7b8ae10ee34bf7e12a9387480d007f309af41
PS: This is not called on Wifi Toggle or AP mode switch