Increase the maximum number of concurrent DNS queries from 32 to 256

This makes the following error message less likely to be printed
when performing many concurrent HTTP requests:

    Condition ' resolving == IP::RESOLVER_INVALID_ID ' is true. returned: ERR_BUG

core/io/ip.h

@@ -56,7 +56,7 @@ public:
 	};
 
 	enum {
-		RESOLVER_MAX_QUERIES = 32,
+		RESOLVER_MAX_QUERIES = 256,
 		RESOLVER_INVALID_ID = -1
 	};