Set DIFF_INTURN to 3

[soc1c]

We discussed this on Discord already, I would strongly suggest having the DIFF_INTURN set to 3.

Short summary: because it is more likely that you have two ouf-of-turn blocks with total score of 2, than three out-of-turn blocks with total score of 3. An in-turn block can help the network to reorganize even if there were two out-of-turn blocks. We had multiple of such occasions that caused Görli network to halt.

ref ethereum#1570 (comment)

[soc1c]

733d502 proposes

• DIFF_INTURN: Block score (difficulty) for blocks containing in-turn signatures. It should be 3 to show a preference over out-of-turn signatures.