net/mlx5: Set QP timestamp mode to default

QPs which don't care from timestamp mode, should set the ts_format
to default, otherwise the QP creation could be failed if the timestamp
mode is not supported.

Fixes: 2fe8d4b8 ("RDMA/mlx5: Fail QP creation if the device can not support the CQE TS")
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>