Announce fail-open mode more aggressively in secchan.

Announce fail-open mode more aggressively in secchan.

Without this change, the secure channel announces that it is
entering or exiting fail-open mode only when an OpenFlow
message actually arrives from the local datapath.  Thus,
when no packets arrive on any switch port, the secchan
never enters fail-open mode.  Functionally, this makes no
difference, because there are no packets to switch anyhow
in that case, but it makes the log harder to interpret
since it's unclear whether the controller connection is
actually up.

With this change, the secure channel announcing that it is
entering or exiting fail-open mode is not tied to receiving
a packet on a switch port.  Thus, the log is easier to
interpret.