lpm: fix condition check in delete

lpm: fix condition check in delete

Fixes an issue of check logic in delete_depth_small function.

For a tbl24 entry, the 'ext_entry' field indicates whether we need
to use tbl8_gindex to read the next_hop from a tbl8 entry, or whether
it can be read directly from this entry.

If a route is deleted, the prefix of previous route is used to override
the deleted route.

When checking the depth of the previous route the conditional checks
both the ext_entry and the depth, but the "else" leg fails to take
account that the condition could fail for one of two possible reasons,
leading to an incorrect flow when 'ext_entry == 0' is true,
but 'lpm->tbl24[i].depth > depth' is false.
The fix here is to add a condition check to the else leg so that it
only executes when ext_entry is set.

Signed-off-by: Na Na <nana.nn@alibaba-inc.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>