KVM: selftests: Support multiple write retires in dirty_log_test

KVM: selftests: Support multiple write retires in dirty_log_test

If dirty_log_test is run nested, it is possible for entries in the emulated
PML log to appear before the actual memory write is committed to the RAM,
due to the way KVM retries memory writes as a response to a MMU fault.

In addition to that in some very rare cases retry can happen more than
once, which will lead to the test failure because once the write is
finally committed it may have a very outdated iteration value.

Detect and avoid this case.

Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20250111003004.1235645-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>