params: allow post-merge hardforks to be enabled before the merge

Partially revert ethereum/go-ethereum#29023.
This commit intentionally breaks the post-merge hardforks logic to fix
the problem described in
#232 (comment).

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

Author: AnnaShaleva

params/config.go

@@ -958,8 +958,6 @@ func (c *ChainConfig) Rules(num *big.Int, isMerge bool, timestamp uint64) Rules
 	if chainID == nil {
 		chainID = new(big.Int)
 	}
-	// disallow setting Merge out of order
-	isMerge = isMerge && c.IsLondon(num)
 	return Rules{
 		ChainID:          new(big.Int).Set(chainID),
 		IsHomestead:      c.IsHomestead(num),
@@ -973,9 +971,9 @@ func (c *ChainConfig) Rules(num *big.Int, isMerge bool, timestamp uint64) Rules
 		IsBerlin:         c.IsBerlin(num),
 		IsLondon:         c.IsLondon(num),
 		IsMerge:          isMerge,
-		IsShanghai:       isMerge && c.IsShanghai(num, timestamp),
-		IsCancun:         isMerge && c.IsCancun(num, timestamp),
-		IsPrague:         isMerge && c.IsPrague(num, timestamp),
-		IsVerkle:         isMerge && c.IsVerkle(num, timestamp),
+		IsShanghai:       c.IsShanghai(num, timestamp),
+		IsCancun:         c.IsCancun(num, timestamp),
+		IsPrague:         c.IsPrague(num, timestamp),
+		IsVerkle:         c.IsVerkle(num, timestamp),
 	}
 }