IB/cma: Check for GID on listening device first

As a simple optimization that should speed up the vast majority of
connect attemps on IB devices, when we are searching for the GID of an
incoming connection in the cached GID lists of devices, search the
device that received the incoming connection request first.  If we
don't find it there, then move on to other devices.

This reduces the time to perform 10,000 connections considerably.
Prior to this patch, a bad run of cmtime would look like this:

connect      :    12399.26   12351.10    8609.00    1239.93

With this patch, it looks more like this:

connect      :     5864.86    5799.80    8876.00     586.49

Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>