[release-v1.7] server: Force PoW upgrade to v9.

This modifies the vote notification logic so that wallets will no longer
vote on mainnet blocks once height 635775 has been reached and the block
version is prior to 9.

This change is being made to make use of the staking system to force
proof-of-work miners to upgrade to the latest version in a timely
fashion so voting on the new consensus changes can commence.

server.go

@@ -2568,7 +2568,7 @@ func (s *server) handleBlockchainNotification(notification *blockchain.Notificat
 		// namely blocks 101, 102, 103, 104, 105, and 106.
 		//
 		// Additionally, a notification will NOT be sent for mainnet once block
-		// height 534304 has been reached and the block version is prior to 8.
+		// height 635775 has been reached and the block version is prior to 9.
 		// The intent is for future code to perform this type of check more
 		// dynamically so it happens for all upgrades after a certain time frame
 		// is provided for upgrades to occur, but it is hard coded for now in
@@ -2579,7 +2579,7 @@ func (s *server) handleBlockchainNotification(notification *blockchain.Notificat
 		blockHeight := int64(blockHeader.Height)
 		reorgDepth := bestHeight - (blockHeight - band.ForkLen)
 		isOldMainnetBlock := s.chainParams.Net == wire.MainNet &&
-			blockHeight >= 534304 && blockHeader.Version < 8
+			blockHeight >= 635775 && blockHeader.Version < 9
 		if s.rpcServer != nil &&
 			blockHeight >= s.chainParams.StakeValidationHeight-1 &&
 			reorgDepth < maxReorgDepthNotify &&