p2p: support using pre-defined passphrase for adding a new P2P group

wpas_p2p_group_add could use pre-defined network, but always generate
passphrase randomly. Provide a way to use pre-defined passphrase.

Bug: 64695709
Test: Group creation
      * create a group with a configuration.
      * join it as new Group Client.
      * join it as new Group Client.

Change-Id: I08fbfd6542a5c1e76335c3a5911ba09ea6d9ca78
2 files changed