[MS10] Address leftover comments on MS03 and MS07

- Fix the copyright year in IPMSDatabase.java.
- Add missing Override annotations.
- Remove random l2keys, use fixed strings.
- Rename the method in OnNetworkAttributesRetrieved that puzzlingly
  nobody noticed was wrong.

Test: atest IpMemoryStoreServiceTest
Bug: 113554482
Change-Id: If71fadd23e158a4be299d112bfce75690b1ed8e8