rocker: Add proper validation of Netlink attributes

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
---
new in v4
rocker: Use logical operators on booleans

Silences various sparse warnings

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
---
new in v4