ntdb: optimize ntdb_fetch.

ntdb: optimize ntdb_fetch.

We access the key on lookup, then access the data in the caller.  It
makes more sense to access both at once.  We also put in a likely()
for the case where the hash is not chained.

Before:
Adding 1000 records: 3644-3724(3675) ns (129656 bytes)
Finding 1000 records: 1596-1696(1622) ns (129656 bytes)
Missing 1000 records: 1409-1525(1452) ns (129656 bytes)
Traversing 1000 records: 1636-1747(1668) ns (129656 bytes)
Deleting 1000 records: 3138-3223(3175) ns (129656 bytes)
Re-adding 1000 records: 3278-3414(3329) ns (129656 bytes)
Appending 1000 records: 5396-5529(5426) ns (253312 bytes)
Churning 1000 records: 9451-10095(9584) ns (253312 bytes)
smbtorture results (--entries=1000)
ntdb speed 183881-191112(188223) ops/sec

After:
Adding 1000 records: 3590-3701(3640) ns (129656 bytes)
Finding 1000 records: 1539-1605(1566) ns (129656 bytes)
Missing 1000 records: 1398-1440(1413) ns (129656 bytes)
Traversing 1000 records: 1629-2015(1710) ns (129656 bytes)
Deleting 1000 records: 3118-3236(3163) ns (129656 bytes)
Re-adding 1000 records: 3235-3355(3275) ns (129656 bytes)
Appending 1000 records: 5335-5444(5385) ns (253312 bytes)
Churning 1000 records: 9350-9955(9494) ns (253312 bytes)
smbtorture results (--entries=1000)
ntdb speed 180559-199981(195106) ops/sec