ethtool: add support to set/get completion queue event size

Add support to set completion queue event size via ethtool -G
parameter and get it via ethtool -g parameter.

~ # ./ethtool -G eth0 cqe-size 512
~ # ./ethtool -g eth0
Ring parameters for eth0:
Pre-set maximums:
RX:             1048576
RX Mini:        n/a
RX Jumbo:       n/a
TX:             1048576
Current hardware settings:
RX:             256
RX Mini:        n/a
RX Jumbo:       n/a
TX:             4096
RX Buf Len:             2048
CQE Size:                128

Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>