lib/classifier: Fix array splicing.

Array splicing was broken when multiple elements were being moved,
resulting in the priority order being mixed.  This came up when the
highest priority rule from a subtable was removed and the subtable
needed to be moved down the priority list by more than one position.

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