net/802: use struct_size over open coded arithmetic

Replace zero-length array with flexible-array member and make use
of the struct_size() helper in kmalloc(). For example:

struct garp_attr {
	struct rb_node			node;
	enum garp_applicant_state	state;
	u8				type;
	u8				dlen;
	unsigned char			data[];
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi (CGEL ZTE) <chi.minghao@zte.com.cn>

net/802/garp.c

@@ -184,7 +184,7 @@ static struct garp_attr *garp_attr_create(struct garp_applicant *app,
 			return attr;
 		}
 	}
-	attr = kmalloc(sizeof(*attr) + len, GFP_ATOMIC);
+	attr = kmalloc(struct_size(*attr, data, len), GFP_ATOMIC);
 	if (!attr)
 		return attr;
 	attr->state = GARP_APPLICANT_VO;

net/802/mrp.c

@@ -273,7 +273,7 @@ static struct mrp_attr *mrp_attr_create(struct mrp_applicant *app,
 			return attr;
 		}
 	}
-	attr = kmalloc(sizeof(*attr) + len, GFP_ATOMIC);
+	attr = kmalloc(struct_size(*attr, value, len), GFP_ATOMIC);
 	if (!attr)
 		return attr;
 	attr->state = MRP_APPLICANT_VO;