hs-v3: Service can pick more than HiddenServiceNumIntroductionPoints intro points
During my testing of legacy/trac#30200 (moved), I ended up with service descriptor with 4 intro points even though
HiddenServiceNumIntroductionPoints is set to 3 (default).
Further investigation confirmed this by adding a log in the
decode_intro_points() function which showed me 4 intro points.
I haven't found out why but one feature of HS is that we launch
HiddenServiceNumIntroductionPoints + 2 intro circuits in parallel and the first one to finish are picked.
It appears that more than the defined value can finish at the same time and will be picked.