ring: guarantee dequeue ordering before tail update

ring: guarantee dequeue ordering before tail update

Consumer queue dequeuing must be guaranteed to be done fully before
the tail is updated. This is not guaranteed with a read barrier,
changed to a write barrier just before tail update which in practice
guarantees correct order of reads and writes.

Signed-off-by: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>