net: ena: Fix rx_copybreak value update

Make the upper bound on rx_copybreak tighter, by
making sure it is smaller than the minimum of mtu and
ENA_PAGE_SIZE. With the current upper bound of mtu,
rx_copybreak can be larger than a page. Such large
rx_copybreak will not bring any performance benefit to
the user and therefore makes no sense.

In addition, the value update was only reflected in
the adapter structure, but not applied for each ring,
causing it to not take effect.

Fixes: 1738cd3e

 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Osama Abboud <osamaabb@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>