iavf: change the flex-byte support number to macro definition

The maximum number (2) of flex-byte support is derived from ethtool
use-def data size (8 byte).

Change the magic number 2 to macro definition, and add the comment to
track the design thinking, so the code is clear and easily maintained.

Signed-off-by: Haiyue Wang <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/iavf/iavf_ethtool.c

···
 	if (!(fsp->flow_type & FLOW_EXT))
 		return 0;
 
-	for (i = 0; i < 2; i++) {
+	for (i = 0; i < IAVF_FLEX_WORD_NUM; i++) {
 #define IAVF_USERDEF_FLEX_WORD_M	GENMASK(15, 0)
 #define IAVF_USERDEF_FLEX_OFFS_S	16
 #define IAVF_USERDEF_FLEX_OFFS_M	GENMASK(31, IAVF_USERDEF_FLEX_OFFS_S)

drivers/net/ethernet/intel/iavf/iavf_fdir.h

···
 	IAVF_FDIR_FLOW_PTYPE_MAX,
 };
 
+/* Must not exceed the array element number of '__be32 data[2]' in the ethtool
+ * 'struct ethtool_rx_flow_spec.m_ext.data[2]' to express the flex-byte (word).
+ */
+#define IAVF_FLEX_WORD_NUM	2
+
 struct iavf_flex_word {
 	u16 offset;
 	u16 word;
···
 };
 
 struct iavf_fdir_extra {
-	u32 usr_def[2];
+	u32 usr_def[IAVF_FLEX_WORD_NUM];
 };
 
 /* bookkeeping of Flow Director filters */
···
 	/* flex byte filter data */
 	u8 ip_ver; /* used to adjust the flex offset, 4 : IPv4, 6 : IPv6 */
 	u8 flex_cnt;
-	struct iavf_flex_word flex_words[2];
+	struct iavf_flex_word flex_words[IAVF_FLEX_WORD_NUM];
 
 	u32 flow_id;