iproute2: ip addr: Organize flag properties structurally

This creates a nice systematic way to check that the various flags are
mutable from userspace and that the address family is valid.

Mutability properties are preserved to avoid introducing any behavioral
change in this CL. However, previously, immutable flags were ignored and
fell through to this confusing error:

Error: either "local" is duplicate, or "dadfailed" is a garbage.

But now, they just warn more explicitly:

Warning: dadfailed option is not mutable from userspace
Signed-off-by: David Ahern <dsahern@gmail.com>
1 file changed