Maintain a single array (of struct with two int variables) instead of
two independent arrays (of int) for tracking know ifindexes and reasons
for having added them. The previous implementation tried to maintain two
independent arrays even though they were always required to be of
exactly same length and order. That had resulted in a bug earlier and
the code was not exactly easy to understand either, so replace this with
a single array.
Signed-off-by: Jouni Malinen <j@w1.fi>