logind: make use of EVIOCSMASK input ioctl to mask out events we aren't interested in

      This way logind will get woken up only when an actual event took place,
and not for every key press on the system.

The ioctl EVIOCSMASK was added by @dvdhrm already in October 2015, for
the use in logind, among others, hence let's actually make use of it
now.

While we are at it, also fix usage of the EVIOCGSW ioctl, where we
assumed a byte array, even though a unsigned long native endian array is
returned.