Detect active chains differently to work around a firmware bug which would mark non-existing chains as active.
Detect active chains differently to work around a firmware bug which
would mark non-existing chains as active.

Obtained from:	OpenBSD
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase