ovs-ofctl: Check min flow format support in negotiate_highest_flow_format().

ovs-ofctl: Check min flow format support in negotiate_highest_flow_format().

When the -F option wasn't set, or if it was set to an invalid flow format
for the match, this code would happily select a flow format that did not
select the user's requested match if the switch didn't support an
advanced-enough flow format.  This fixes the problem.  It also changes
behavior in the case where the user specifies a flow format that cannot
represent the match, changing this from a warning to a fatal error; this
is consistent with -F behavior for flow_mod commands.