devlink: fix referencing namespace by PID

devlink: fix referencing namespace by PID

netns parameter for devlink reload is supposed to take PID
as well as string name. However, the PID parsing has two
bugs:
 - the opts->netns member is unsigned so the < 0
   condition is always false;
 - the parameter list is not rewinded after parsing as
   a name, so parsing as a pid uses the wrong argument.

Fixes: 08e8e1ca3e05 ("devlink: extend reload command to add support for network namespace change")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@gmail.com>