fix captive portal prune sessions, radius still needs work, old code copied back but not sure if this works

LOG_AUTH is not a level, it's a facility which can't be cherry-picked
from the syslog() call.  Remove it.  Also stops spewing of auth message
into console.

Discussed with: Jos

Since this might break a few setups I'll postpone the zap
until after releasing the next snapshot on our road to 15.1.

The platform information should be used to identify a platform
type, not the product name.  Not sure why pfSense came up with
this, but now it's so deeply tied into the system that we can't
just take it out.  The platform type is also steered by the
installer or build tools at the moment.  We will change that,
but it'll take more testing.

Discussed with: Jos