Add mostly-static checks on consistency of Equihash parameters, MAX_HEADERS_RESULTS, and MAX_PROTOCOL_MESSAGE_LENGTH.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

src/main.h

@@ -94,6 +94,10 @@ static const unsigned int DATABASE_FLUSH_INTERVAL = 24 * 60 * 60;
 /** Maximum length of reject messages. */
 static const unsigned int MAX_REJECT_MESSAGE_LENGTH = 111;
 
+#define equihash_parameters_acceptable(N, K) \
+    ((CBlockHeader::HEADER_SIZE + equihash_solution_size(N, K))*MAX_HEADERS_RESULTS < \
+     MAX_PROTOCOL_MESSAGE_LENGTH-1000)
+
 struct BlockHasher
 {
     size_t operator()(const uint256& hash) const { return hash.GetCheapHash(); }