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/crypto/equihash.h

@@ -155,6 +155,10 @@ class EhSolverCancelledException : public std::exception
 
 inline constexpr const size_t max(const size_t A, const size_t B) { return A > B ? A : B; }
 
+inline constexpr size_t equihash_solution_size(unsigned int N, unsigned int K) {
+    return (1 << K)*(N/(K+1)+1)/8;
+}
+
 template<unsigned int N, unsigned int K>
 class Equihash
 {