linux-gen: pktio: fix flexible array member error in pedantic compila…

…tion

When compiling with GCC 13.1 and -Wpedantic, struct sset_info causes
the error "invalid use of structure with flexible array member
[-Werror=pedantic]". The flexible array member in this case is the
data member of struct ethtool_sset_info. In order to reserve space for
it, turn sset_info into a union, and make the next member in the union
the size of struct ethtool_sset_info and the data.

Signed-off-by: Jere Leppänen <jere.leppanen@nokia.com>
Reviewed-by: Janne Peltonen <janne.peltonen@nokia.com>

platform/linux-generic/pktio/stats/ethtool_stats.c

@@ -29,9 +29,11 @@
 
 static struct ethtool_gstrings *get_stringset(int fd, struct ifreq *ifr)
 {
-	struct {
+	union {
 		struct ethtool_sset_info hdr;
-		uint32_t buf[1]; /* overlaps with hdr.data[] */
+		/* Reserve space for hdr.data. */
+		uint8_t buf[sizeof(struct ethtool_sset_info) +
+			    sizeof(((struct ethtool_sset_info *)0)->data[0])];
 	} sset_info;
 	struct ethtool_drvinfo drvinfo;
 	uint32_t len;