agent: Require use of "SCD DEVINFO --watch" command with socket.
* agent/call-scd.c (agent_card_devinfo): Check if client connects by a socket.
(cherry picked from commit c4ff9c5def1aaf76f7cec82d9aa7e5cb1b77f044)
- GnuPG-bug-id: T7151
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>