net: ena: update ena documentation

The PCI vendor IDs in the documentation inaccurately describe the ENA
devices. For example, the 1d0f:ec20 can have LLQ support. The driver
loads in LLQ mode by default, and a message is printed to the kernel
ring if the mode isn't supported by the device, so the device table
isn't needed.

Also, LLQ can support various entry sizes, so the documentation is
updated to reflect that.

Interrupt moderation description is also updated to be more accurate.

Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>