use Ref in getipaddr and improve type stability

[stevengj]

Just a slight improvement I noticed when I was doing something else.

[stevengj]

AppVeyor failure seems to be #16555.

[stevengj]

Merging, since this seems uncontroversial.

[tkelman]

what about this improves type stability?

[yuyichao]

Not reassigning a variable to a different type. This is the known limitation of type inference/codegen that generates inefficient code for type unstable variable even though each use of the variable have a leaftype.

[stevengj]

Yeah, unfortunately it's a quite common pattern to do

function foo(x)
   x = canonicalize(x)
   ...
end

so that x changes type.