gpg: Use ephemeral mode for generating card keys.
* g10/call-agent.c (agent_set_ephemeral_mode): New. * g10/keyedit.c (keyedit_menu) <bkuptocard>: Switch to ephemeral mode. * g10/keygen.c (do_generate_keypair): Switch to ephemeral mode for card keys with backup.
- GnuPG-bug-id: T6944