After the link tests, there is a race on one side of the test for
the link coming up. It's possible, in some cases, for the test script
to write to the 'peer_trans' files before the link has come up.

To fix this, we simply use the link event file to ensure both sides
see the link as up before continuning.
Signed-off-by: NLogan Gunthorpe <logang@deltatee.com>
Acked-by: NAllen Hubbe <Allen.Hubbe@dell.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>
Fixes: a9c59ef7 ("ntb_test: Add a selftest script for the NTB subsystem")