Function copy_data

tools/lightning-downgrade.c:42–45

};

static void copy_data(u8 **out, const u8 *in, size_t len)
{
	tal_arr_appendn(out, in, len);
}

/* askrene added DSTORE_CHANNEL_BIAS_V2 (convertable) and
 * DSTORE_NODE_BIAS (not convertable) */