mcq-network-pftable: fixed typo

The second OutPort of R1 is at the East.

Note: about the previous one:

> Upon reception of this packet, the port forwarding table of `R3` will be updated as :

>      ======  ========
>      Dest.   OutPort 
>      ======  ========
>      A       N 
>      B       E 
>      ======  ========

I guess it's wrong too but I don't know how to fix it: by adding an edge between `R3` and `B`?