axgbe: Use the common RSS key without options RSS

Fetch the common key in the PCI iflib frontend regardless of options RSS
and make the key API declaration available in both configurations.
Retain the existing hash-field selection and queue-placement branches.
The independent ARM frontend is unchanged.

Reviewed by:	gallatin
MFC after:	2 weeks
Sponsored by:	BBOX.io
Differential Revision:	https://reviews.freebsd.org/D59794

sys/dev/axgbe/if_axgbe_pci.c

@@ -59,8 +59,8 @@
 #include "opt_inet6.h"
 #include "opt_rss.h"
 
-#ifdef RSS
 #include <net/rss_config.h>
+#ifdef RSS
 #include <netinet/in_rss.h>
 #endif
 
@@ -723,13 +723,17 @@ axgbe_initialize_rss_mapping(struct xgbe_prv_data *pdata)
 {
 	int i;
 
-	/* Get RSS key */
 #ifdef	RSS
 	int	qid;
 	uint32_t	rss_hash_config = 0;
+#endif
 
+	/* Get RSS key independently of software RSS queue placement. */
+	_Static_assert(sizeof(pdata->rss_key) == RSS_KEYSIZE,
+	    "RSS key size mismatch");
 	rss_getkey((uint8_t *)&pdata->rss_key);
 
+#ifdef	RSS
 	rss_hash_config = rss_gethashconfig();
 
 	if (rss_hash_config & RSS_HASHTYPE_RSS_IPV4)
@@ -739,8 +743,6 @@ axgbe_initialize_rss_mapping(struct xgbe_prv_data *pdata)
 	if (rss_hash_config & RSS_HASHTYPE_RSS_UDP_IPV4)
 		XGMAC_SET_BITS(pdata->rss_options, MAC_RSSCR, UDP4TE, 1);
 #else
-	arc4rand(&pdata->rss_key, ARRAY_SIZE(pdata->rss_key), 0);
-
 	XGMAC_SET_BITS(pdata->rss_options, MAC_RSSCR, IP2TE, 1);
 	XGMAC_SET_BITS(pdata->rss_options, MAC_RSSCR, TCP4TE, 1);
 	XGMAC_SET_BITS(pdata->rss_options, MAC_RSSCR, UDP4TE, 1);