ofproto: Fix potential leak during flow mods.

This code created a cls_rule without destroying it.  Found by
inspection.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
ofproto: Fix is_flow_deletion_pending() false positive.

If one tries to install a rule that's identical to another rule in
another OpenFlow table which is being deleted, it's possible that
is_flow_deletion_pending() might confuse them and block the
installation.  This is such an edge case I doubt it has ever actually
happened.

Found by inspection.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>