The correct OID format for CTLTYPE_U64 is `QU` (`uquad_t`), not `A`
(text expressed via `char *`).
This issue was noticed while doing an sysctl tree walk using a
sysctl(9) consumer that relies on the OID format to intuit what the
type should be for a given sysctl.
MFC after: 1 month
Sponsored by: DellEMC Isilon
Differential Revision: https://reviews.freebsd.org/D34877