applyShareRealityParams and SubJsonService.realityData generated a fresh
random spx on every export, so share links, "export all links", and JSON
subscriptions never matched a spiderX configured on the inbound and two
exports of the same client disagreed with each other. Read the value from
realitySettings.settings like pbk/fp/pqv and keep the random value only as
a fallback when none is configured.
Closes#5718