macvlan: remove unused fields in struct macvlan_dev

commit 635b8c8e ("tap: Renaming tap related APIs, data structures,
macros") captured all the tap related fields into a new struct tap_dev.
However, it failed to remove those fields from struct macvlan_dev.
Those fields are currently unused and must be removed. While there
I moved the comment for MAX_TAP_QUEUES to the right place.

Fixes: 635b8c8e

 (tap: Renaming tap related APIs, data structures, macros)
Signed-off-by: Girish Moodalbail <girish.moodalbail@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>