net: pktgen: fix mpls maximum labels list parsing

Fix mpls maximum labels list parsing up to MAX_MPLS_LABELS entries (instead
of up to MAX_MPLS_LABELS - 1).

Addresses the following:

	$ echo "mpls 00000f00,00000f01,00000f02,00000f03,00000f04,00000f05,00000f06,00000f07,00000f08,00000f09,00000f0a,00000f0b,00000f0c,00000f0d,00000f0e,00000f0f" > /proc/net/pktgen/lo\@0
	-bash: echo: write error: Argument list too long

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/core/pktgen.c

@@ -900,6 +900,10 @@ static ssize_t get_labels(const char __user *buffer, struct pktgen_dev *pkt_dev)
 	pkt_dev->nr_labels = 0;
 	do {
 		__u32 tmp;
+
+		if (n >= MAX_MPLS_LABELS)
+			return -E2BIG;
+
 		len = hex32_arg(&buffer[i], 8, &tmp);
 		if (len <= 0)
 			return len;
@@ -911,8 +915,6 @@ static ssize_t get_labels(const char __user *buffer, struct pktgen_dev *pkt_dev)
 			return -EFAULT;
 		i++;
 		n++;
-		if (n >= MAX_MPLS_LABELS)
-			return -E2BIG;
 	} while (c == ',');
 
 	pkt_dev->nr_labels = n;