Fix Wstringop-overflow warning from util/srp.cpp (#6855)

* Fix Wstringop-overflow warning from util/srp.cpp

src/util/srp.cpp

@@ -38,6 +38,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdint.h>
 
 #include <config.h>
 
@@ -417,7 +418,7 @@ static SRP_Result H_nn(
 }
 
 static SRP_Result H_ns(mpz_t result, SRP_HashAlgorithm alg, const unsigned char *n,
-	size_t len_n, const unsigned char *bytes, size_t len_bytes)
+	size_t len_n, const unsigned char *bytes, uint32_t len_bytes)
 {
 	unsigned char buff[SHA512_DIGEST_LENGTH];
 	size_t nbytes = len_n + len_bytes;