lpm: remove redundant check when adding rule

lpm: remove redundant check when adding rule

When a rule with depth > 24 is added into an existing
rule with depth <=24, a new tbl8 is allocated, the existing
rule first fulfill whole new tbl8, so the filed valid of
each entry in this tbl8 is always true and depth of each
entry is always <= 24 before adding the new rule with depth > 24.

Signed-off-by: Wei Dai <wei.dai@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>