scd: Don't inhibit SSH authentication for larger data if it can.
* scd/app-openpgp.c (do_auth): Use command chaining if available.
Cherry-picked from master branch of:
e8fb8e2b3e66d5ea8a3dc90afdc14611abf2c3da
- GnuPG-bug-id: T5935
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>