realtek: add cond_resched to loops accessing the FDB table

A full loop accessing all FDB entries can take several milliseconds
(on RTL839x about 20 ms), so give other kernel tasks a chance to run.
This is especially important for rtl83xx_port_fdb_dump which is itself
called in a loop for all ports by the kernel.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>

target/linux/realtek/files-5.15/drivers/net/dsa/rtl83xx/debugfs.c

@@ -343,6 +343,9 @@ static int l2_table_show(struct seq_file *m, void *v)
 
 		seq_printf(m, "Hash table bucket %d index %d ", bucket, index);
 		l2_table_print_entry(m, priv, &e);
+
+		if (!((i + 1) % 64))
+			cond_resched();
 	}
 
 	for (i = 0; i < 64; i++) {