thermal: netlink: Rename thermal_gnl_family

Almost all thermal netlink structures use thermal_genl prefix.
Change thermal_gnl_family name accordingly for consistency.

No functional impact.

Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>