kdf:pkdf2: Require longer input when FIPS mode.
* cipher/kdf.c (_gcry_kdf_pkdf2): Add length check.
Cherry-pick master commit of:
857e6f467d0fc9fd858a73d84122695425970075
- GnuPG-bug-id: T6039
- Fixes-commit: ab5aef9b7b6ef757eff7bea4a17ade0ce3d3191b
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>