Improve handling of BIP9Deployment limits

Small tweaks by Pieter Wuille.

src/consensus/params.h

@@ -7,6 +7,7 @@
 #define BITCOIN_CONSENSUS_PARAMS_H
 
 #include "uint256.h"
+#include <limits>
 #include <map>
 #include <string>
 
@@ -31,6 +32,9 @@ struct BIP9Deployment {
     int64_t nStartTime;
     /** Timeout/expiry MedianTime for the deployment attempt. */
     int64_t nTimeout;
+
+    /** Constant for nTimeout very far in the future. */
+    static constexpr int64_t NO_TIMEOUT = std::numeric_limits<int64_t>::max();
 };
 
 /**