fail-open: Drop some of the weirder special cases.

fail-open: Drop some of the weirder special cases.

I don't have any real evidence that these special cases make a difference
in real-world cases.  The messages for the commits that add them are not
clear about the reasons for them.  I seem to recall that they were only
tested with the dummy controller inside OVS, which isn't very good evidence
for real controllers.  Finally, they cut across layers in nasty ways and
make it hard to better abstract packet-ins and packet buffering.

If these solve real problems then we can reconsider after some reports
come in.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Jarno Rajahalme <jarno@ovn.org>