[perfnet] engine block downloader stuck on shadow forks #15877

problem is that when we send out "get header requests" over devp2p with sentry we always send it to the same 5 peers (due to a max limit of 5 peers when sending the message out) which causes issues for shadow forks:

• in a shadow fork environment we have very few peers that are on the shadow fork (e.g. 5 bootnodes) and majority of the other peers we are connected to are mainnet peers (the shadowfork uses the same networkid=1 as mainnet)
• what ended up happening is that we would always hit the same 5 peers that were on mainnet instead of the shadowfork when trying to backward sync using the EL block downloader