rfkill: allow to get the software rfkill state

iwlwifi needs to be able to differentiate between the
software rfkill state and the hardware rfkill state.

The reason for this is that iwlwifi needs to notify any
change in the software rfkill state even when it doesn't
own the device (which means even when the hardware rfkill
is asserted).

In order to be able to know the software rfkill when the
host does not own the device, iwlwifi needs to be able to
ask the state of the software rfkill ignoring the state
of the hardware rfkill.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Link: https://lore.kernel.org/r/20211219195124.125689-1-emmanuel.grumbach@intel.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>