secchan: Clarify log message about failing open.

secchan: Clarify log message about failing open.

In commit e10dfcf357 "rconn: Be pickier about what constitutes a
successful connection", the criteria for determining a successful
OpenFlow connection was tightened.  When rconn connects at a socket
level, it prints messages stating that it "connected" and the switch is
taken out of fail-open mode.  If it is determined that it is not a
"successful" OpenFlow connection, then the connection is closed and
fail-open is re-enabled.  When this occurs, fail-open logs the following
potentially confusing message:

    Could not connect to controller for XXX seconds, failing open

Where XXX is the number of seconds since the last "succesful" connection
rather than simple socket-level connection.  This commit changes the
message to:

    Could not establish OpenFlow channel to controller for XXX
    seconds, failing open

Bug #1163