Allow the InfiniBand RC retry count to be configured by the user as an
option in the target login string.  Reducing this retry count allows to
reduce the path failover time.
Signed-off-by: NVu Pham <vu@mellanox.com>

[ bvanassche: Rewrote patch description / changed default retry count ]
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Acked-by: NDavid Dillow <dillowda@ornl.gov>
Signed-off-by: NRoland Dreier <roland@purestorage.com>