DPL: more prerequisites for earlier forwarding

[ktf]

In principle this is not fatal because the number of routes is always
larger / equal than the number of channels by construction.

Better safe than sorry.

[github-actions]

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[ktf]

Given #14910 still does not work, let's merge some safe parts of it.

[ktf]

ARM Linux issue unrelated and will be fixed by alisw/alidist#6086.