s3/smbd: change locking behavior when "lock spin time = 0".

s3/smbd: change locking behavior when "lock spin time = 0".

The "lock spin time" parameter mimics the following Windows
setting which by default is 250ms in Windows and 200ms in Samba.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\LockViolationDelay

When a client sends repeated, non-blocking, contending BRL requests
to a Windows server, after the first Windows starts treating these
requests as timed blocking locks with the above timeout.

As an efficiency, I've changed the behavior when this setting is 0,
to skip this logic and treat all requests as non-blocking locks.

This gives the smbd server behavior similar to the 3.0 release with
the do_spin_lock() implementation.

I've also changed the blocking lock parameter in the call from
push_blocking_lock_request() to true as all requests made in this
path are blocking by definition.