net: ena: fix driver when PAGE_SIZE == 64kB

[ Upstream commit ef5b0771d247379c90c8bf1332ff32f7f74bff7f ]

The buffer length field in the ena rx descriptor is 16 bit, and the
current driver passes a full page in each ena rx descriptor.
When PAGE_SIZE equals 64kB or more, the buffer length field becomes
zero.
To solve this issue, limit the ena Rx descriptor to use 16kB even
when allocating 64kB kernel pages. This change would not impact ena
device functionality, as 16kB is still larger than maximum MTU.

Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>