net: ena: improve ENA driver boot time.

The ena admin commands timeout is in resolutions of 100ms.
Therefore, When the driver works in polling mode, it sleeps for 100ms
each time. The overall boot time of the ENA driver is ~1.5 sec.
To reduce the boot time, This change modifies the granularity of
the sleeps to 5ms.
This change improves the boot time to 220ms.

Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>