ofproto-dpif: Propagate may_enable flag as link aliveness.

ofproto-dpif: Propagate may_enable flag as link aliveness.

The idea is to use OFPPS_LIVE bit to propagate link aliveness state
towards the controller also when sending port status.  The
ofport->may_enable flag could be used for this purpose, thus any
change in LIVE bit is propagated towards conrtoller in
OFPT_PORT_STATUS message.  OFPPS_LIVE bit is set only when links is
not down not administratively, neither operationally as recommended
in OF papers.  I added 9 new unit tests to verify link state changes
when monitored with cfm, bfd or lacp for OF 1.3, OF 1.4 and OF 1.5.
I updated related unit tests according to the changes of
ofproto-dpif.

Signed-off-by: László Sürü <laszlo.suru at ericsson.com>
Co-authored-by: Zoltán Balogh <zoltan.balogh at ericsson.com>
Signed-off-by: Zoltán Balogh <zoltan.balogh at ericsson.com>
Co-authored-by: Jan Scheurich <jan.scheurich at ericsson.com>
Signed-off-by: Jan Scheurich <jan.scheurich at ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>