tests/bsim bis: Reduce the test verbosity

The test was printing one line for each packet it was sending
by default. That creates a huge log and slows things down.
Instead, let's only print those with verbosity set at 4 or higher.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

tests/bsim/bluetooth/ll/bis/src/main.c

@@ -183,7 +183,7 @@ static void iso_send(struct k_work *work)
 	iso_data_len = MAX(sizeof(seq_num), ((seq_num % CONFIG_BT_ISO_TX_MTU) + 1));
 	net_buf_add_mem(buf, iso_data, iso_data_len);
 
-	printk("ISO send: seq_num %u\n", seq_num);
+	bs_trace_info_time(4, "ISO send: seq_num %u\n", seq_num);
 	ret = bt_iso_chan_send(&bis_iso_chan, buf, seq_num++,
 			       BT_ISO_TIMESTAMP_NONE);
 	if (ret < 0) {