add interface-used

[piccione99]

We want to be able to send the network interface we are using to connect in the convey header. It seems like we will need to explicitly try each network interface until one works. And define and order of priority to try interfaces. Unless there is a better way.

In order to do this:

1. it looks like we will need to create a custom http client with it's own net.Dialer.
2. Loop through each network interface until one works.
3. for each attempt, the network interface we are trying needs to be available as input to the convey header