Randomize same priority service groups

[mxinden]

When there are multiple services, and thus multiple groups, with the same priority, the client SHOULD shuffle these groups randomly.

https://ietf-wg-happy.github.io/draft-happy-eyeballs-v3/draft-ietf-happy-happyeyeballs-v3.html#section-5.2

[mxinden]

Bugzilla tracking: https://bugzilla.mozilla.org/show_bug.cgi?id=2039248