Randomize extra_nonce

To guarantee that hashing blobs will be different between different p2pool nodes, even if they mine to the same wallet address and don't have transactions to shuffle within the block template.

src/stratum_server.h

@@ -103,6 +103,7 @@ private:
 
 	struct BlobsData
 	{
+		uint32_t m_extraNonceStart;
 		std::vector<uint8_t> m_blobs;
 		size_t m_blobSize;
 		uint64_t m_target;