ethtool: add netlink attr in rss get reply only if value is not null

ethtool: add netlink attr in rss get reply only if value is not null

Current code for RSS_GET ethtool command includes netlink attributes
in reply message to user space even if they are null. Added checks
to include netlink attribute in reply message only if a value is
received from driver. Drivers might return null for RSS indirection
table or hash key. Instead of including attributes with empty value
in the reply message, add netlink attribute only if there is content.

Fixes: 7112a04664bf ("ethtool: add netlink based get rss support")
Signed-off-by: Sudheer Mogilappagari <sudheer.mogilappagari@intel.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Link: https://lore.kernel.org/r/20230111235607.85509-1-sudheer.mogilappagari@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>