sysctl: use correct types and names in sysctl_*sec_to_sbintime

The functions are intended to report kernel variables that are
stored as sbintime_t (pointed to by arg1) as human readable
nanoseconds or milliseconds (reported via sysctl_handle_64).
The variable types and names were reversed. I guess there is
no functional change here, as all types flipped around were
signed 64. Note that these function aren't used yet anywhere
in the kernel.

Reviewed by: mav
Differential revision: https://reviews.freebsd.org/D38217