lib/classifier: Optimize megaflows for single rule case.

lib/classifier: Optimize megaflows for single rule case.

When, during a classifier lookup, we narrow down to a single potential
rule, it is enough to match on ("unwildcard") one bit that differs
between the packet and the rule.

This is a special case of the more general algorithm, where it is
sufficient to match on enough bits that separates the packet from all
higher priority rules than the matched rule.  For a miss that would be
all the rules.  Implementing this is expensive for a more than a few
rules.  This patch starts by doing this for a single rule when we
already have it, also reducing the lookup cost by finishing the lookup
earlier than before.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>