use native SYSCTL_TYPE__CTL_32 and SYSCTL_TYPE__CTL_STR

v2: add BUILD_BUG_ONS to check SysctlType constants are equal to
__CTL_STR and CTL_32, change __CTL_STR to CTL_STR in SysctlType enum.
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>