test/nvmf_timeout: Reduce TCP Ack timeout

By the default value, timeout might be too long to detect connection
failure by the end of the test. 512 milliseconds is too small to use
in production but is not so small for this case.

Fixes #2595

Signed-off-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Change-Id: I9f1248b2812eb7625aa943878b022f0a151d4cbb
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/13908


Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Reviewed-by: Dong Yi <dongx.yi@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Michal Berger <michal.berger@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>