linux-next-cherry-picks: RDMA/ucma.c: Different fix for ucma context uid=0, causing...

linux-next-cherry-picks: RDMA/ucma.c: Different fix for ucma context uid=0, causing iWarp RDMA applications to fail in connection establishment

Fix for ucma context uid=0, causing iWarp RDMA applications to fail in connection establishment.

This is a new patch addressing the librdmacm segfault when RDMA_CM_EVENT_ESTABLISHED event shows up with evt->id_priv = NULL
In the ucma_event_handler(), ctx->file->mut is moved up to prevent race conditions and protect from assigning zero ucma ctx->uid to asynchronously generated events.

Signed-off-by: Tatyana Nikolova <Tatyana.E.Nikolova@intel.com>
Signed-off-by: Sean Hefty <Sean.Hefty@intel.com>
Signed-off-by: Vladimir Sokolovsky <vlad@mellanox.com>