packet: reorder a member in packet_ring_buffer

There's a 4 byte hole in packet_ring_buffer structure before
prb_bdqc, that can be filled with 'pending' member, thus we can
reduce the overall structure size from 224 bytes to 216 bytes.
This also has the side-effect, that in struct packet_sock 2*4 byte
holes after the embedded packet_ring_buffer members are removed,
and overall, packet_sock can be reduced by 1 cacheline:

Before: size: 1344, cachelines: 21, members: 24
After:  size: 1280, cachelines: 20, members: 24
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/packet/internal.h

@@ -54,6 +54,7 @@ struct pgv {
 
 struct packet_ring_buffer {
 	struct pgv		*pg_vec;
+
 	unsigned int		head;
 	unsigned int		frames_per_block;
 	unsigned int		frame_size;
@@ -63,8 +64,9 @@ struct packet_ring_buffer {
 	unsigned int		pg_vec_pages;
 	unsigned int		pg_vec_len;
 
-	struct tpacket_kbdq_core	prb_bdqc;
 	atomic_t		pending;
+
+	struct tpacket_kbdq_core	prb_bdqc;
 };
 
 extern struct mutex fanout_mutex;