In case the consensus parameters for the rate/burst changes, we need to update
all already established introduction circuits to the newest value.

This commit introduces a "get all intro circ" function from the HS circuitmap
(v2 and v3) so it can be used by the HS DoS module to go over all circuits and
adjust the INTRODUCE2 token bucket parameters.

Signed-off-by: David Goulet <dgoulet@torproject.org>