Addrman: only shuffle as much as we need.
Addrman: only shuffle as much as we need.

If we switch the knuth shuffle to the version that swaps the element
with an element between it and the end of the array, then once we have
gotten to the amount of elements we need they won't change later in the
algorithm. Terminating here means that we only do 23% of the length of
the array worth of random swaps at most.

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