Add a memory barrier before setting an inline data segment's byte count

Add a memory barrier before setting an inline data segment's byte count

We need a memory barrier before setting an inline segment byte count
to make sure that all the inline data for a cacheline has been written
before changing the cacheline's byte-count from 0xffffffff to
something valid.

Signed-off-by: Ishai Rabinovitz <ishai@mellanox.co.il>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>