rfkill: add master_switch_mode and EPO lock to rfkill and rfkill-input

rfkill: add master_switch_mode and EPO lock to rfkill and rfkill-input

Add of software-based sanity to rfkill and rfkill-input so that it can
reproduce what hardware-based EPO switches do, blocking all transmitters
and locking down any further attempts to unblock them until the switch is
deactivated.

rfkill-input is responsible for issuing the EPO control requests, like
before.

While an rfkill EPO is active, all transmitters are locked to one of the
BLOCKED states and all attempts to change that through the rfkill API
(userspace and kernel) will be either ignored or return -EPERM errors.

The lock will be released upon receipt of EV_SW SW_RFKILL_ALL ON by
rfkill-input, or should modular rfkill-input be unloaded.

This makes rfkill and rfkill-input extend the operation of an existing
wireless master kill switch to all wireless devices in the system, even
those that are not under hardware or firmware control.

Since the above is the expected operational behavior for the master rfkill
switch, the EPO lock functionality is not optional.

Also, extend rfkill-input to allow for three different behaviors when it
receives an EV_SW SW_RFKILL_ALL ON input event.  The user can set which
behavior he wants through the master_switch_mode parameter:

master_switch_mode = 0: EV_SW SW_RFKILL_ALL ON just unlocks rfkill
controller state changes (so that the rfkill userspace and kernel APIs can
now be used to change rfkill controller states again), but doesn't change
any of their states (so they will all remain blocked).  This is the safest
mode of operation, as it requires explicit operator action to re-enable a
transmitter.

master_switch_mode = 1: EV_SW SW_RFKILL_ALL ON causes rfkill-input to
attempt to restore the system to the state before the last EV_SW
SW_RFKILL_ALL OFF event, or to the default global states if no EV_SW
SW_RFKILL_ALL OFF ever happened.   This is the recommended mode of
operation for laptops.

master_switch_mode = 2: tries to unblock all rfkill controllers (i.e.
enable all transmitters) when an EV_SW SW_RFKILL_ALL ON event is received.
This is the default mode of operation, as it mimics the previous behavior
of rfkill-input.

In order to implement these features in a clean way, the entire event
handling of rfkill-input was refactored into a single worker function.

Protection against input event DoS (repeatedly firing rfkill events for
rfkill-input to process) was removed during the code refactoring.  It will
be added back in a future patch.

Note that with these changes, rfkill-input doesn't need to explicitly
handle any radio types for which KEY_<radio type> or SW_<radio type> events
do not exist yet.

Code to handle EV_SW SW_{WLAN,WWAN,BLUETOOTH,WIMAX,...} was added as it
might be needed in the future (and its implementation is not that obvious),
but is currently #ifdef'd out to avoid wasting resources.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Dmitry Torokhov <dtor@mail.ru>