learning-switch: Don't use exact-match on every field by default.

learning-switch: Don't use exact-match on every field by default.

OVS has all kinds of odd fields, e.g. registers, and it doesn't make sense
to try to match on all of them.  This commit changes learning-switch to
only try to match on the fields defined by OpenFlow 1.0.  That's still not
minimal, but it's more reasonable.

This commit should not have an immediately visible effect since
ovs-controller always sends OF1.0 format flows to the switch, and OF1.0
format flows don't have these extra fields.  But in the future when we
add support for new protocols and flow formats to ovs-controller, it
will make a difference.

Signed-off-by: Ben Pfaff <blp@nicira.com>