Add more logic for robust caching

1. After successful service discovery, save the hash and database
2. Before service discovery, read db first
  - if an existing database has the same hash value, directly
    apply the database, and back to connected state
  - otherwise, start service discovery immediately
3. Point addr file to hash file by hard link
4. For bonded devices, if there is no database hash on them,
   directly load existing cache. (Backward compatibility)

Bug: 154056389
Test: compile & verify gatt client behavior
Tag: #feature
Change-Id: I0a7655b3734906ae47adb66890683c9c68ff728a