WifiNetworkSuggestionsManager: Persist enterprise credentials

Enterprise credentials for suggestions were not being persisted to disk.
This would prevent the device from auto-connecting to networks suggested
by apps (via the new network suggestion API surface) after a reboot.

Bug: 136088495
Test: atest com.android.server.wifi
Test: ACTS test: NetworkSuggestionTest
Test: Verified scenario mentioned in the bug (carrier wifi app suggested
EAP networks not connecting).

Merged-In: Ife2cff3daf84a5986cb2b63207eccf1b6faee5ae
Change-Id: Ife2cff3daf84a5986cb2b63207eccf1b6faee5ae
2 files changed