mbuf: move leaf_rcv union farther back in the pkthdr

When the leaf_rcv union was introduced to support ktls RX offload in
4d88d81c31 it was put at the front of the pkthhdr, and pushed the
more commonly accessed csum_flags and rsstype into the next cacheline.

Given that csum_flags is accessed on every pkt sent and every pkt freed,
but the leaf_rcv fields are only used for ktls rx offload, it makes more
sense to have csum_flags in a cacheline that is already likely to be hot.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D60691
Sponsored by: Netflix

sys/sys/mbuf.h

@@ -157,13 +157,6 @@ struct pkthdr {
 			uint16_t rcvgen;	/* ... and generation count */
 		};
 	};
-	union {
-		struct ifnet	*leaf_rcvif;	/* leaf rcv interface */
-		struct {
-			uint16_t leaf_rcvidx;	/* leaf rcv interface index ... */
-			uint16_t leaf_rcvgen;	/* ... and generation count */
-		};
-	};
 	SLIST_HEAD(packet_tags, m_tag) tags; /* list of packet tags */
 	int32_t		 len;		/* total packet length */
 
@@ -176,6 +169,13 @@ struct pkthdr {
 #if !defined(__LP64__)
 	uint32_t	 pad;		/* pad for 64bit alignment */
 #endif
+	union {
+		struct ifnet	*leaf_rcvif;	/* leaf rcv interface */
+		struct {
+			uint16_t leaf_rcvidx;	/* leaf rcv interface index ... */
+			uint16_t leaf_rcvgen;	/* ... and generation count */
+		};
+	};
 	union {
 		uint64_t	rcv_tstmp;	/* timestamp in ns */
 		struct {