net: ena: add support for changing max_header_size in LLQ mode

Up until now the driver always used a single setting for the sizes
of the different parts of the llq entry - 128 for entry size, 2 for
descriptors before header and 96 for maximum header size.

The current code makes sure that the parts of the llq entry are
compatible with each other and with the initial llq entry size given
by the device.

This commit changes this code to support any llq entry size

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>