Relax PBKDF2 iteration check for FIPS self-test

Relax PBKDF2 iteration check for FIPS self-test

FIPS 140-3 IG 10.3.A.8 requires known-answer tests for KDFs. Some of these
tests for PBKDF2 use a low iteration count (e.g., 2) which is below the normal
security threshold and would otherwise fail.

This change checks if a PBKDF2 self-test is in progress and, if so, lowers the
minimum accepted iteration count to 2. This allows the required self-tests to
pass while maintaining the security check for normal operations.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/29222)