Merge branch 'nsid-cleanup' into next

Guillaume Nault  says:

====================

It's currently hard to review ipnetns. The netns ids are inconsistently
treated as signed or unsigned and most helper functions aren't prepared
to use negative ids.

Netns id attributes can be negative: NETNSA_NSID_NOT_ASSIGNED =3D=3D -1.
So let's consistently treat nsids as signed and also reject negative
values in functions that are supposed to only handle assigned netns
ids.

While there, let's drop the extra blank line generated by some command
line parsing errors (patch 5/5).

====================

Signed-off-by: David Ahern <dsahern@gmail.com>