realtek: dsa: Build check size of drop counter names

The commit 1cfd45ae0bad ("realtek: Add debugfs support for RTL9300") caused
previously an out of bounds access on the array holding the names of drop
counters (and incorrect names in the output) fur RTL839x because of a
missing comma. To avoid such situation in the future, calculate the size of
the array during compilation. And to ensure that this count matches the
actual number of counters in HW, compare this number during compile time
with the expected value.

Suggested-by: Hauke Mehrtens <[email protected]>
Signed-off-by: Sven Eckelmann <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20905
Signed-off-by: Robert Marko <[email protected]>

target/linux/realtek/files-6.12/drivers/net/dsa/rtl83xx/debugfs.c

@@ -205,22 +205,26 @@ static ssize_t drop_counter_read(struct file *filp, char __user *buffer, size_t
 	case RTL8380_FAMILY_ID:
 		d = rtl838x_drop_cntr;
 		offset = RTL838X_STAT_PRVTE_DROP_COUNTERS;
-		num = 40;
+		num = ARRAY_SIZE(rtl838x_drop_cntr);
+		BUILD_BUG_ON(num != 40);
 		break;
 	case RTL8390_FAMILY_ID:
 		d = rtl839x_drop_cntr;
 		offset = RTL839X_STAT_PRVTE_DROP_COUNTERS;
-		num = 45;
+		num = ARRAY_SIZE(rtl839x_drop_cntr);
+		BUILD_BUG_ON(num != 45);
 		break;
 	case RTL9300_FAMILY_ID:
 		d = rtl930x_drop_cntr;
 		offset = RTL930X_STAT_PRVTE_DROP_COUNTERS;
-		num = 85;
+		num = ARRAY_SIZE(rtl930x_drop_cntr);
+		BUILD_BUG_ON(num != 85);
 		break;
 	case RTL9310_FAMILY_ID:
 		d = rtl931x_drop_cntr;
 		offset = RTL931X_STAT_PRVTE_DROP_COUNTERS;
-		num = 81;
+		num = ARRAY_SIZE(rtl931x_drop_cntr);
+		BUILD_BUG_ON(num != 81);
 		break;
 	}