net: ena: Change license into format to SPDX in all files

All ena files should now use SPDX format in their license string. This
doesn't change the license of the files, but rather states the same
license in fewer words.

Also update the license years in some of the files.

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