s3:g_lock: avoid very expensive generate_random_buffer() in g_lock_parse()

s3:g_lock: avoid very expensive generate_random_buffer() in g_lock_parse()

We don't require a sequence number that is incremented,
we just need a value that's not reused.
We use the new generate_unique_u64(), which is much cheaper!

Using smbtorture3 //foo/bar -U% local-g-lock-ping-pong -o 500000
under valgrind --tool=callgrind...

This change replaces this:

 13,129,925,659  PROGRAM TOTALS

  4,125,752,958  ???:_nettle_sha256_compress [/usr/lib/x86_64-linux-gnu/libnettle.so.6.4]
  1,257,005,866  ???:_nettle_aes_encrypt [/usr/lib/x86_64-linux-gnu/libnettle.so.6.4]
    590,000,773  bin/default/../../lib/tdb/common/lock.c:tdb_lock_list
    571,503,429  ???:_nettle_aes_set_key [/usr/lib/x86_64-linux-gnu/libnettle.so.6.4]
    479,000,608  bin/default/../../lib/tdb/common/lock.c:tdb_unlock
    ...

by this:

  6,877,826,377  PROGRAM TOTALS

    590,000,773  bin/default/../../lib/tdb/common/lock.c:tdb_lock_list
    479,000,608  bin/default/../../lib/tdb/common/lock.c:tdb_unlock
    ...
     12,500,033  bin/default/../../lib/util/genrand_util.c:generate_unique_u64
    ...
     8,996,970  ???:_nettle_sha256_compress [/usr/lib/x86_64-linux-gnu/libnettle.so.6.4]

time smbtorture3 //foo/bar -U% local-g-lock-ping-pong -o 5000000

gives:

   537426 locks/sec

  real    0m19,071s
  user    0m15,061s
  sys     0m3,999s

vs.

   900956 locks/sec

  real    0m11,155s
  user    0m8,293s
  sys     0m2,860s

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>