Code review comment for lp:~andreas-pokorny/mir/fix-1531517

LGTM. For my changes ill just be hard coding an uint8_t[20] for the mac, sooo this wont cause me any issues. Which will just give me a operator= copy/move for the mac anyway soo no fancy changes needed on my end here.

Sooo really depends on whos branch lands first :), should be a simple conflict (if any)

One things:
+#include <unordered_set>
+ std::unordered_set<size_t> sent_indices;

Doesnt seem to be used?