eal/windows: fix default thread priority

eal/windows: fix default thread priority

The hard-coded thread priority for Windows threads in EAL
is REALTIME_PRIORITY_CLASS/THREAD_PRIORITY_TIME_CRITICAL.

This results in issues with DPDK threads causing OS thread starvation
and eventually a bugcheck.

The fix reduce the thread priority to
NORMAL_PRIORITY_CLASS/THREAD_PRIORITY_NORMAL.

Bugzilla ID: 600
Fixes: 53ffd9f080f ("eal/windows: add minimum viable code")
Cc: stable@dpdk.org
Reported-by: Odi Assli <odia@nvidia.com>
Signed-off-by: Tal Shnaiderman <talshn@nvidia.com>
Acked-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>