netlink: add netlink handler for gcoalesce (-c)

Implement "ethtool -c <dev>" subcommand using ETHTOOL_MSG_COALESCE_GET
netlink message. This retrieves and displays device coalescing parameters,
traditionally provided by ETHTOOL_GCOALESCE ioctl request.

Unlike the ioctl code, netlink can distinguish between unsupported
parameter (shown as "n/a") and zero value ("0" or "off").

Also register the callback with monitor code so that the monitor can
display ETHTOOL_MSG_COALESCE_NTF notifications.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
6 files changed