bridge: Change port's 'ifaces' member from array to list.

bridge: Change port's 'ifaces' member from array to list.

In my opinion, this makes the code more obviously correct in many places,
because there are generally fewer variables.  One must generally keep two
variables in sync for iterating through an array: the array index and the
contents of the array at that index.  For iterating through a list, only
the list element is necessary.