toggle ZSL mode properly

D2's camera HAL is very stupid and it leaves camera_mode on even when
ZSL has been turned off.

Change-Id: If2216c8f7ae40ad272fb6048d955b3f99a46f6fe
fix this mess

camMode and ZSL are persistent across camera switches and switches from
still video to camcorder, resulting in inconsistent states.

The fix:
Don't just detect if camMode is unset, since the previous set state is
too persistent. Instead, test specifically for the special mode Snapchat
sets that the wrapper would never set, where the recording hint is not
on but camMode is.

Ensure we are only enforcing the Hangouts exception for the FFC.

Restore the previous ZSL logic. It worked just fine.

Change-Id: I0751c12ebd4035a86682e9c9c76b7e2d422cbc7e