wpa_supplicant(hidl): Add set/get for eap private key id

"private_key" field is not used in Android, we instead use the
"key_id" field. So, change the setter to reflect that.

While there,
Set an empty string for eap phase2 method if it's set to none. This is
what is being done currently in the socket interface.

Bug: 35663125
Test: Compiles
Test: Able to connect to Hotspot 2.0 networks.
Change-Id: Ic193fb3606a9e35a3fe3dba36117201d2500183c
2 files changed