macvlan: fix memory hole in macvlan_dev

Move 'macaddr_count' from after 'netpoll' to after 'nest_level' to pack
and reduce a memory hole.

Fixes: 88ca59d1 (macvlan: remove unused fields in struct macvlan_dev)
Signed-off-by: Girish Moodalbail <girish.moodalbail@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>