rgw: initialize rgw_log_entry::identity_type
uninitialized identity_type field was causing unit test failures from
check-generated.sh:
**** rgw_log_entry test 2 dump_json check failed ****
ceph-dencoder type rgw_log_entry select_test 2 dump_json > /tmp/typ-AW7AEODB3
ceph-dencoder type rgw_log_entry select_test 2 encode decode dump_json > /tmp/typ-0NX4cmLHR
21c21
< "identity_type":
3599295712
---
> "identity_type":
2072560864
Fixes: https://tracker.ceph.com/issues/58115
Signed-off-by: Casey Bodley <cbodley@redhat.com>